Ooh, I like this thread--will have to see if there are any hidden gems listed!
My top five
1. It's Okay That's Love
-- Realistic and a beautifully, simple drama (with a bit of angst.) Slice-of-life for the most part with very very real and relatable characters.
2. King2Hearts
It's been a long time, but I remember it's a super solid and interesting drama, even down to the politics. Love the character dynamics.
3. Missing Noir M
Love the classier feel of this OCN drama (and awaiting a second season!) It's an episodic crime drama but it also made me cry at the end of many cases.
4. Thank You
Super sweet and mellow. It's a bit slice-of-lifey but mostly on the drama side, and the relationships between the characters is beautiful.
5. Signal
Probably been listed a bunch already but it's amazing. A really great mix of drama, crime, suspense, and fantasy (let's not get into the time travel mechanics though...)
Bonus: Evil Minds (Chinese)
Firstly, the episodes are only 30 minutes long, so that's great. If you love crime and psychological games, an can handle a bit of blood in some gruesome cases, I think you ASBOLUTELY MUST WATCH this drama.