Mystery/crime kdramas

• Blind 
• Confession 
• Memorist 
• The Game: Towards Zero 
• Train 

ohhhh this is right up my alley. I am a hugeeee crime/thriller fan. :)
Though exciting and crime are two words that are difficult. Most gems in crime land are slow and take time but are sooo damn well done for that.
Though I am actually a bit surprised. You have not seen some of the most well known crime dramas (at least not listed in your watchlist) Thus I will give you first some quite popular crime dramas and then some lesser known ones.
Either way some recs;

Not underrated but are not on your list:
Signal - gotta say Im very surprised you haven't seen Signal. Signal is THE crime drama and far away from underrated,  so defo check this out first.
Tunnel - as my fellow commenters recommended you, tunnel is really a nice drama. Very similar to Signal.
King of Pig's 
Stranger 
Children of Nobody 
Through the Darkness

Some underrated dramas:
Watcher - this starts slow, though it is a GEM of a crime drama with so many twists and turns. No character is good and all have their own agenda. Truly a great crime drama.
Nobody Knows
Tell me What you saw - this is lacking something but it is a gripping crime drama so defo give it a try.
Lies Within
Children of a Lesser God
Lies Hidden in my Garden - this is more arthouse? But super good and very bizarre
Hometown 
Somebody - pure arthouse drama. A serial killer falls in love with a genius but she is kinda crazy herself. This is very very specific. Pure arthouse. But a great drama for thriller fans.


I must say, as an absolut crime/thriller fan, korean crime dramas are not as well developed as Chinese or Taiwanese dramas are. There are some gems (like Signal) but overall I highly highly highly recommend you to check out Chinese and Taiwanese thriller/crime dramas (highly recommend you here the Light on Series). 

• Nobody knows
• Voice
• Tunnel
• Children of nobody
• Mouse
• Hello Monster
• The Guest
• He is psychometric 
• The cursed
• Stranger
• Mad dog
• Lookout

Replying because I want to know more kdramas of this genre.

Circle: 2 worlds connected - Haven't watched in a long time but I'm pretty sure it had really good plot twists.