Hyena
A drama that pretty much fires on all cylinders from the word "Go", the writing, the perfomances, the worldbuilding are pretty much aces from the first episode.

World of the Married
An artistic, highbrow take on the makjang drama that does an excellent job at setting up the trashy rollercoaster that will follow for the following 15 episodes, its also far superior to its british original imo ( Surrane Jones was absolutely fantastic in the original though)

The most recent ones that I can recall having great first episode are:
Extraordinary Attorney Woo
Taxi Driver 2

What a fun prompt! I can't wait to read everyone's answers. A short list of what I would consider great first episodes to great dramas includes:
Like Flowers in Sand
The Matchmakers
Bossam: Steal the Fate
Mr. Queen
Healer
I would also add, for my personal preferences of greatness/first episodes, Unlock My Boss and Into the Ring. While I wouldn't say I loved the whole drama, While You Were Sleeping has an EXCELLENT first episode, too.

Money Flower

The list is endless but...

Trolley
Queenmaker
Why Her?
Our Blues - I pressed play on this solely because of the first 3 episodes.
Uncle Samsik - You have to watch this to know this.
Queen For Seven Days: This one is beyond the first episode. The introductory minutes alone is something else.
Arthdal Chronicles 1.
Tell Me That You Love Me.
The World of the Married.
Cheat on Me If You Can.
Behind Every Star: Jo Yeo-jung and Seo Hyun-woo sold this drama to me with their bickering chemistry in episode 1. The people who matched that bickering chemistry again in the show was Park Ho-san and Oh Na-ra.
Adamas.

Perfect Marriage Revenge it was prefect from the get-go. 🤣🤣🤣

Episode 1 wasted no time, set up all characters, we knew what we could expect and wowza 😱 did it deliver. 🙌

Mr. Sunshine
Young Eugene (Kim Kang-hoon’s) performance was just amazing.

Happiness
I blindly jumped into this without watching any teasers and all I can say is the lead’s instant chemistry is probably one of the best I’ve seen in the last few years.

I haven’t watched all of it, and I’ll definitely get back to it at some point but the first episode of MY LIBERATION NOTES is incredible.

I’ll also add ATYPICAL FAMILY as well, it’s pilot episode is confusing and yet unique and intriguing, pretty much as the title suggests ATYPICAL

*And just a note: don’t get caught up in thinking about great dramas with crappy first episodes yet — we’ll be chatting about that next time.

LOL
And we need crappy dramas with great first episodes as well 😂

The opening of HAPPINESS is both bonkers and immediately establishes the OTP's respective characters. Can't ask for more than that from a first episode.

I also loved the first episode of ROOKIE HISTORIAN GOO HYE-RYEUNG with the OTP's hilarious meet-cute in the bookshop and where we get a very clear picture of how awesome the FL is.

Healer.

This is a gimme, but I'll take it. That first training scene in the hideout (video game tennis, of all things)...straight into the subway/train spy action with Ajumma.

I was there from the first seconds.

I remember Alchemy of Souls having a really fun first episode. It has a lot of history to establish right off the bat but doesn't falter as it moves into the present, and then the introduction of our two leads was just glorious. We know who Jang Uk is immediately, and Naksu/Mu-deok is at her most murderous. We get amazing interactions with Uk being held at crab-leg-point and telling Mu-deok she has beautiful (soul-shifty) eyes. His request at the end that she be his master is an incredible intro to the rest of the whole story. Makes me want to rewatch right away!

Kingdom - they had my complete attention right from the title opening credits. It really was a terrific opening right from ep 1.

This is very interesting. Because with many of my favorite shows I skip the first episode on rewatches.

A Korean Odyssey. That might be partly because I grew up watching Monkey, so I was giggling at a contemporary Monkey, Pigsy, and Sandy even without any story. (Bull Demon King was an extra character, but done so well he had me giggling too)

So many :
- Goblin : I need Gong Yoo in a sageuk!
- A Piece of Your Mind : I loved the atmosphere of this drama.
- Extraordinary You : the world of manhwa with Danoh discovering she's not the FL.
- Heartless City : just for Jung Kyung-ho knife fight.
- Start-Up : Nam Da-reum was too good as the SML's backstory. It ruined the whole drama.
- Castaway Diva : these teenagers were very good, I could have watched a whole drama with them.
- The Matchmakers : It was so beautiful and funny.

The first episode of While You Were Sleeping is a self-contained movie.

Getting back to my list, I was surprised that there are countable ones that fit the bill.
Under The Queen's Umbrella
Bloody Heart
Extraordinary Attorney Woo
Tomorrow
Our Blues
Me Sunshine
Twenty Five Twenty One minus the ending
Call it love minus the time jump
My Dearest 1
Doctor Cha
Flex X Cop
Me Queen
Kairos
Defendant (I am 4 episodes in but I added it to my favorites)
Little Women

Under the Queen's Umbrella. I was sold from the first minute!

It is a very big call for a great first episode - which normally comes around episodes 2 - 4.

Since no one has mentioned it, I’d say One More Happy Ending hit that rare note of getting you in the first 60 minutes. I was so enthralled by that very first episode as we saw the opposite-attract meet of Jung Kyung-ho and Jang Nara, getting drunk together to marriage registration - all within 24 hours. So charming and funny! I was thinking what an amazing first episode and looking forward to a nice romcom….but no.

I would rewatch it every now and then - but only the first episode to re-live that great promise.

D-Day had a pretty unforgettable opening episode. And I thought Flex x Cop did a great job setting up the characterizations in it’s first episode.

I don't have a good memory for details, but I still remember how I was impressed by the cinematography and how one scene morphed into another in It Is OK to Not Be OK.

Interestingly, most kdramas truly take off in Ep2-3, not the very first one. Esp older shows where those initial episodes were all about setup/flashbacks. Take LOVELY RUNNER for example - it's not like Ep1 was objectively weak or anything, but people really got invested after the twist in Ep2. Plus sooo many sageuks that are better with their prequels than actual story - GU FAMILY BOOK, MOON EMBRACING THE SUN... legion of them!

Since people already mentioned HAPPINESS, I'd go with FLOWER OF EVIL, that opening episode was fire (look, PD who knows how to do tension and cliffhangers!). Now that we're talking about it, BEYOND EVIL (precisely Ep1 ending) was quite good too. Right, THE CROWNED CLOWN! All the titles we already mentioned these days))) REVENANT too. I also loved THE FIERY PRIEST's one but I'm probably in minority here... Right, k-SUITS! Another PD with a solid vision. ARANG AND THE MAGISTRATE as well.

For cdramas - TILL THE END OF THE MOON says hello, that intro alone should be in fantasy genre textbooks. Also counts for the most epic introduction scene of ML - twice in the same episode, 3 times in the whole show because tiny LYX can outrizz a crowd without breaking a sweat^^

Yumi's cells would be one of them, no doubt. Amazing drama with an almost perfect script.

Other dramas with a great first episode which kept being very good until the end:

_ Prison Playbook. Wonderful from the first minutes.
_ At a distance, spring is green.
_ Twinkling Watermelon.
_ Live up to your name.
_ The Nokdu Flower (such a powerful and hard start).
_ My Dearest. (But the best episode was the sixth).
_ The Atypical Family (this drama got better from the fourth episode, though).
_ Weak Hero Class 1.
_ My Ahjussi (currently watching it for the first time. 7 out of 16 so far. But my favorite episode has been the first one).

One of the best first episodes I have ever watched is from Start-up, but even though I really like that drama, I think the first episodes were above the rest.

I just rewatched Yumi's cells and it really was that good, just as I remembered. The other standout first episodes for me were The Producers, Racket boys, Hospital Playlist and Reply 1988.

Often I find dramas take a few episodes to get rolling, but Twinkling Watermelon was the most recent one that grabbed me right from the start. I also loved the initial episodes of Search WWW, although I found the rest of the drama a bit more hit or miss. For non-k-dramas, I really liked how A Journey to Love jumped right into the middle of the action and never let up. It was also incredibly efficient at introducing each character in ways that showed us rather than told us about their personalities and the challenges they faced.

Hyena
Under the Queen's Umbrella
My Secret Terrius

Live Up to Your Name 

Life on Mars
Crash Landing on You (I'm among the minority who were satisfied with the way it ended.)

I have two episodes to go on A Shop for Killers. It grabbed me from the very start, and up to this point hasn't let go. Please, show—don't let me down! 🙏🏻

- Arthdal Chronicles (mostly S2, though S1's first episode is good too)
- Parasyte: The Grey
- Taxi Driver
- Extraordinary Attorney Woo
- Marry My Husband

And probably a lot more, but I'm keeping it to my top 10 dramas, or recent dramas, otherwise the list would be too long.

C-dramas
Lost You Forever, Season 1
The Longest Promise
Both of these dramas had a wonderful and very talented child actor/actress cast that really set the stage and presented a really solid foundation for the rest of the story and drama to unfold as the drama transitioned to it’s adult cast. Hypothetically, if a drama were to be made featuring just the child talents of these 2 dramas, I’d be glued to my seat from beginning to finish— they were just that good!! 🥰

Save Your Last Dance for Me (circa 2004/05)
An oldie but a goodie, this drama did well despite it being a drama from the early 2000s wherein that was the era of tropes and makjang galore. This drama did well in presenting said makjang-y tropes in a very concise and to-the-point manner, rather than dragging everything out much like the dramas of those times (seriously, some dramas of that era would and could drag out a trope for the entirety of the drama sheesh), and used the tropes much more as a diving board to the rest of the unfolding of the drama than anything else, and it definitely worked in it’s favour

Marriage Contract
This drama could be seen as a mishmash of the aforementioned two above, in the sense that it has an extremely talented child actress portraying the daughter of the FL (portrayed by Uee), but also has some trope-y characteristics (e.g. Rich playboy ML and financially struggling FL), but again, it works because everything presented in it’s premiere episode is done in a clean and concise manner that helps set the stage for the rest of the drama, but not overtake it

Angel Eyes
Just watch the first 11 (12?) episodes of this drama with the teenage cast (Kang Ha Neul and Nam Ji Hyun) and that’s really all you need from this drama— they were just that good 😍 Honestly, even when I’d gotten to the adult (i.e. main cast) parts of the drama, the acting and the story, and the setup that was given to us via the younger cast just stole my heart completely and I just wasn’t able to get into the rest of the drama once they were off my screen even though the adult cast (Lee Sang Yoon, Gu Hye Sun, Kim Se Jeong) wasn’t necessarily bad in their acting in any way (I KNOW!!! GHS is good in a drama? She surprised me, too tbvh)

All in all, I think it can be said that the general consensus as to what I personally think is an element to a good First Episode(s) to a drama lies heavily on a young talented cast that truly does simply act their hearts out with raw and real emotions and whom aren’t so tied up with how they look— I’d even go as far to say that their looks is probably the last thing on their minds as they’re delving headfirst into the roles they’ve so beautifully gifted me heart ♥️

I'm Sorry I Love You

Goblin - i wanted to see the saguek scenes
Mr Queen - it set up the story really well
Queen for Seven Days - i love the cinematography and childhood scenes
Our Beloved Summer - I love the high school scenes and documentary style
Bossam: Steal the Fate - I like how they introduced the characters and set up the story

Healer: It literally only took five minutes for me to be completely hooked all the way through. That first episode is a microcosm of everything the series would offer: action, suspense, mystery, romance with insane chemistry, and great characters. Excellent final cliffhanger shot as well.

My Liberation Notes: I was skeptical that this show would live up to the hype, but as I watched the first episode, I knew I was going to love it when even during extended scenes of people eating and not talking I was spellbound.

The Smile Has Left Your Eyes: I know not everyone agrees that this is a great drama, but I was hooked from start to finish thanks to SIG's enigmatic, sexy, and ultimately tragic performance. The first episode is dark, mysterious, confusing, and so compelling I immediately re-watched it after finishing the final scene. I had so many questions about who these people were, what they wanted, and whether or not I should trust them. And as the drama unfolded, I only grew more obsessed with getting the answers.

My Dearest: From the first shot, I could tell this production was made with a great deal of care--and money. Gorgeous costumes, music, sets only enhanced the clever dialogue and "GWTW" vibes. The second half wasn't quite as compelling as the first, but I'd still define this as a truly stellar drama.

Seven Days Queen: That opening shot of the queen heading to the gallows was masterful, and the drama really never let up all through its 20 episodes. Tragically romantic, but somehow not depressing, everything about this drama grabbed me and wouldn't let go.

The top of my list - Happiness, Extraordinary Attorney Woo and Under The Queen's Umbrella have already been mentioned, so I will go with two more that left a very strong impression and made me want to keep going:
Business Proposal
Just Between Lovers

I think EAW probably has the best start because it not only tugs on the heart strings, but it deep dives into the heart of it right away. And of course those whales.....

Goblin
Lovely runner
Mr. Sunshine
See you in my 19th life
Attorney Woo
Castaway Diva
My Ahjussi
Forest of Secrets
White Christmas
Circle: Two Worlds
Pretty Noona who buys me food
Fated to love you
Gaus electronics
Korean Odyssey
Romantic Teacher Doctor Kim
Moonlight drawn by clouds
Hotel Del Luna
Tale of the nine tailed—1 and 2
Red sleeve

These are the shows I remember I was on board the first episode. Whether it was cinematography, acting, or just a gestalt of high quality production, these all had that spark that I would have bet money would have been great dramas. And I’ve been right more times than not—except pretty noona, that one burned.

This is a great topic, as one of my main complaints about kdramas are the first episodes. So Healer is the first one that comes to mind, as I think of it as a City Hunter remake with a much better first episode. Another Oh Hae-Young comes to mind, as does Forest of Secrets, and Let's Eat. They all do a nice job of setting the tone for the rest of the series.

Sticking to ones that have yet to be mentioned.
Awaken: great idiosyncratic character played by Namgoong Min, and a very intriguing mystery.
Signal: starting with the ending is tricky, but it paid off here in spades.
Moving: I fell in love with the teenage protagonists first.
Extraordinary You: original premise, great protagonist in Kim Hye-yoon.
Bulgasal: haunting and harrowing origin story that sets up the rest of the series beautifully.
Our Beloved Summer: loved these two characters from the get-go.
Dali and the Cocky Prince: don't know if it was a great first episode, but it was funny, and sexy, and I love seeing strong men completely smitten at first sight.

Signal (I prefer the Korean remake to the US drama somehow)
On the Verge of Insanity (This feels like the Korean version of a marriage between the UK Office and the <IT Crowd but actually written by someone who's got a clue about programming and hardware tech)
Korean Odyssey (by far one of the strongest and tightest plot by the Hong sisters, and the actual source material is so fun too...)
The 8 Show (Oh those gorgeous little opening sequences paired with the insanity of the opening credit music! You'll need to acknowledge the source material before jumping to this one and accept that this is a marriage of Big Brother and Lord of the Flies - I've seen a lot of hate but I feel approaching it with the right mindset can make a big difference; this is one for those who enjoyed Strangers from Hell too because the descent into human darkness is fast)
Moving (from the first scene, you know you'll be in for a cinematographic treat)

Probably many others, but right now nothing else comes to mind!

Well, almost all of my faves were mentioned from "another oh heayoung" to "little women" and Mr. Sunshine, "prison playbook" and "cruel city" and "yumi cells" and....
But I'm here to say, what's that grabbed me in episode 1 of Romantic doctor S1 was the Kiss. imo, it was not just a kiss it was THE kiss!! 😅😂
The best kdrama kiss ever!
It was so delicious that I stayed all throughout the medical things (I usually avoid them in dramas) Just to watch this couple. Their chemistry was out of this world.

In September, 2019 I wrote about PEGASUS MARKET: "I like the first episode because of its absurd humor. It had a Monty Python stitched skits together quality to the show. I just wonder how the show can keep up the intensity level of the first episode." Well, it did and more through each succeeding episode.

I second Hyena here, but my favourite-first-episodes-of-a-consistently-great-show are the ones of "Piece of your mind" and "Chief Kim".
I particularly loved the first episode of Piece of your Mind and won't ever skip it on a rewatch. It is so beautifully filmed, it has an airy feel to it and wonderful colours. What I found most intriguing on my first ever watch was that I had no idea where this show was going. In most dramas, k or not, you see the characters and the setting and you know who will end up with whom and what obstacles they'll have to overcome, or what the general message of it all will be. Here it was just very open. I love/d it! And I love Chae Soo-bin and Jung Hae-in in it, they are just the right cast for this drama.
With Chief Kim in the first episode are just the first great scenes of many more to come, and it might just be the funniest art of introduction you'll ever see in a kdrama. 😁

I consider most of my top 10 best kdramas in this list. But there's just something special about My Mister. The show is dark, depressing, and real from the get go that it wrings my heart and I just can't let go.

Oohhhh, that could be a long list for me. Since I am a not a fan of waiting everyday drama, nowadays I always wait until series is finish/like 12 eps aired before sat down and watch. First 2 eps that really caught my attention and great until finale:

Designated Survivor: 60 Days
Lovely Runner
While you were sleeping
Kingdom
Queen for 7Days
Under Queen Umbrella
It's Okay to Not be Okay

Castaway Diva imo was a great drama and has an amazing first episode. I think even people that disliked it loved the first episode.

*Flower of Evil*

I will always toot this horn

Amazing First Episode? Say Less!
(Disclaimer: not all of these dramas are my favorites, their first episodes just intrigued me)

1. Hwayugi - the little with the yellow umbrella, Son Oh Gong's Baby Boy Car 😂, Ma Wang! The first episode hooked me.

2. Romance is a Bonus Book - the bride ran away from her wedding and her best friend (who is obviously in love with her) went to get her back? Shut up and take my money!!!

3. Goblin - the first clip of the flower fields switching to night and a bloodied rusty sword with EL's voiceover 🤤🤤

4. The Moon Embracing the Sun - the meet cute at the beginning and my first time seeing a hanbok 🥰🥰🥰

5. The Matchmakers/Under the Queen's Umbrella - the colorful setting and the characters

6. Oh My Ghostess - wow. Just wow. Especially since I had zero expectations 🥹