My top 5:

1. Master's Sun! I really thought this drama was extremely unique in terms of dramaland plot lines and I enjoyed the comical ghost scenes. I liked how there was more to the story then simply romance such as facing your fears and accepting yourself. I rather enjoyed the ending and liked the over all character developments and that you could see each character evolve throughout the episodes. while some dramas can make you lose interest after so many episodes, this drama kept my interest every episode and made me wonder what would happen next. I've watched it at least five times and still enjoy it.

2. Empress Ki! I loved how the plot mainly focused on revenge and duty with a side of romance. The character's were never really detestable (well the villains were but that was the point) and I loved how they started out awesome and simply leveled up in amazing like a freakin pokemon. It was more than romance with an interesting tale of vengeance, justice, duty, and loyalty. She's probably still one of my favorite heroines of all time (the real empress ki might not have been so noble but the dramaland empress ki sure knew how take down her foes with one fell swoop)

3. 49 days! The plot for this one was perfect! It was very unique and had me crying and laughing with every episode. It was heartbreaking and heartwarming all at the same time. There were a lot of valuable life lessons in it and while the ending was devestating and extremely unfair, I found also that it’s what ultimately made the drama. While it might have seemed unfair, I believe the point was that she had a chance to find people who genuinely cared about her and spend her final days with those who sincerely loved her which made her seemingly sad fate seem more fortunate than tragic.  

4. Miss Ripley! I loved the realistic feel to this drama. The plot line was brilliant and perfectly depicted human nature in general. I loved how the heroine was different from your typical female leads and felt she was more sincere in a twisted kind of way. This was ironic since it was built around her lies, but her character was more honest in itself than most drama leads. I loved how the characters weren’t solid black or white but were many shades in between so that they didn’t seem just ‘villain’ or ‘victim’ but instead fit somewhere in between becoming ‘human’ instead. There were so many life lessons and tragedies in this that I could never completely hate the female lead in this, I instead cried with her and felt pity for all of her suffering and hardships. This drama was brilliant in depicting how a person who had never been given love can become lost and unsure of what is right in their quest for happiness. It was devastating but I loved how honest it felt.

  5. Jewel in the Palace! I loved how the story immediately drug you in. You practically grew up with the character and watched her life take place. I felt her pain and her happiness with every episode and loved how there wasn’t just one huge plot line but multiple side plotlines intertwining making it complex and dynamic. The characters matured with every obstacle and I loved how romance didn’t entirely consume the plot line. The romance in this was absolutely beautiful (one of the most beautifully developed romances I’ve seen in a drama actually. I truly felt like these two were in love). I also liked how the main lead had ambition and a desire to get stronger. The ending in this was absolutely perfect. I really hope they make a second one!
My Top Five Kdramas:

1. Incomplete Life/Misaeng
2. Reply 1997
3. The Princess' Man
4. Healer
5. Bridal Mask/Gaksital
1. Fated to Love You (Korean Version)
2. Kill Me, Heal Me
3. Good Doctor
4. Secret
5. The Queen's Classroom (Korean Version)

Coming close... Innocent Man
1) Reply 1997. this drama totally captivated me. i think i've never watched whole series as fast as this one. fantastic actors and coming of age story really get to me
2) 49days. (i'm really surprised to see it mentioned only once) it was quite different and very enjoyable. and the ending was so. good.
3) Marriage, not dating. i'm a sucker for pretend relationship dramas and this was the best of them. han groo was so likable despite the fact i wouldnt usually like character like hers. also the chemistry between main characters was one of the bests i've seen so far
4) Shut up: flower boy band. i really liked the focus on friendship + very good soundtrack

(honorable mention: Cinderella's sister. i know its very melodramatic and draggy but i love first 4 episodes with story before time-skip)
((i'm not here to start some fanwars or something but i'm quite shocked some of you are mentioning playful kiss as i found this drama (or at least korean ver) very average))
A few of you have mentioned reply1997..think that will be next on my list..

my all time fave kdramas are 

1. You who came from the stars - this is the series that got me interested in kdramas again, think the last one I watched before that was like coffee prince..I loved the chemistry of the leads and loved the storyline..i ended up watching it twice in one week, then I moved on to all his other dramas and films

2. Master's sun - was a bit skeptical about this but my boyfriend saw it recommended on YouTube and made me watch it with him..and I'm glad he did..the storyline was funny and the mains were awesome..my bf loved it and has a man crush on so ji sub..haha

3. My lovely Sam soon - one of the earlier dramas I've seen, fun to watch and lovable characters

4. The girl who sees smell - again I was a bit skeptical, especially with a title like that, and again my bf wanted to watch it after he found out it adapted from a webtoon, got me hooked from the very first episode and we manage to watch the second half of the series in one sitting! I fell in love with park yoo chun after this and is now making my way through his older series :)

5. Let's eat 2 - I didn't see the first one but decided to give this a try because I love food. This was very easy to watch and I loved the characters and all he food they showcased. I tried to watch let's eat 1 after but the lead actress didn't do it for me so have dropped it.

honarable mentions - moon embracing the sun and rooftop prince, winter sonata and stairways to heaven 
1.Coffee Prince
2.Gokusen
3.Reply 1997
4.It's Okay,That's Love
5.Healer

1- It's Okay That's Love
2- Boys Over Flowers
3- God's Gift - 14 Days
4- Cruel City (The Heartless City)
5- 49 Days and Gu Family Book
1- Kill me heal me
2 - You Who Came from the Stars
3 - Innocent Man
4 - Goong 
5 - 49 Days

This is proper hard. TBH i have trouble ranking them but as a guess my top 5 so far to date (out of 105)

1. HEALER
2. KILL ME HEAL ME
3 CITY HALL
4. MASTERS SUN
5. PASTA
5.5 SMILE, YOU

If J-Dramas are allowed to be included i'd also add in Hana Kimi (it's so so so funny) and for T-dramas i'd add in Just you
1. Healer - I just absolutely fell in love with the acting, writing, OST's, and the plot. This drama is damn near perfect. The ending is well written, and doesn't leave me angry, in fact it was pretty darn great! The cast was stellar, they knew their characters so well. It's got some action, some romance, epic twists and turns, starry eyed actors, and a plot that always knocks you off of your feet!
2. Good Doctor - The portrayal of autism by Joo Won was truly spectacular. The script, the plot, the actors were all equally moving. Watching this drama, I cried many many times, sometimes out of frustration for Joo Won's character, sometimes out of pure joy. It's truly a beautiful and well made story with an ending that makes me smile and a story that warms my heart.
3. Sungkyukwan Scandal - This was the first historical drama I ever watched, it made me laugh, cry, and giggle. Although it's not the most outstanding of all dramas I've seen, it is such a warm story. The characters endless life and the plots sweet pick me up tune always bring me back for more. And the overall lesson that knowledge and education are for everyone, not just those few born more privileged than the rest. 
4. It's Okay, That's Love - The storyline, and cast really pulled off this smart, and endearing tale of overcoming mental illness and finding strength in yourself. The actors were flawless in their delivery of their characters. The depth and emotion brought to Jang Jae Yeol by Jo In Sung is not something I've seen in many dramas. 
5. Marriage Not Dating - This drama steals my last spot with its warmth and charisma. A story seemingly like so many others, but full of surprises, and so much endless warmth. I couldn't stop watching this drama. It was well done, and the acting really pushed it over the top. I believed in the characters and in the story. 
My top 5 Kdramas are the ff:

1. Sungkyunkwan Scandal
2. Goong
3. Healer
4. Coffee Prince
5. Jang geum
(Not in order because it would honestly be too difficult to puzzle together)
A Gentleman's Dignity: because it was hilarious and it even had some cute romance :')

The Suspicious Housekeeper: It was super interesting and I was really surprised with this drama.

Kill Me, Heal Me: It has some really funny parts and the main male lead is a GREAT actor. The romance was sweet to but more than that...the characters acted out by Ji Sung were so well portrayed and developed. This is a must watch if you haven't already.

Incomplete Life: This drama felt like a documentary and that's what I loved about it, it's so different from the typical drama in every way. It lacked music, that made it feel incomplete (which in my opinion is a good thing because of the title), and the romance was only hinted but I guess you can basically assume what will happen after the end. I fell in love with Si Won because of this. (No...not super junior, sorry)

The King of Dramas: This was funny and it had a lot of romance. This one does have Super Junior's Si Won, lucky you. I liked this one because it appealed to my interest in an interesting way. I was very curious about the process of drama making during this time. (but the drama isn't a documentary of course, it's not informational about it)
My Top 5 today... although tomorrow it most likely will change ;-)

1. Fated to love you
2. The Master's Sun
3. Let's Eat
4.Chuno
5. Queen In-Hyun's Man
Kill me heal me
High school savvy
Healer
Modern farmer
Big
My Top 5 K-dramas are:

1. You are Beautiful
2. Mawang
3. The Greatest Love
4. Wonderful Life
5. Angry Mom