I looked to my wachlist and found, that from korean dramas I mostly watched only those with romance. But I found few with no romance:
Nightmare Teacher - this is quite good mystery horror
The Guardians - this is also good action, thriller, crime drama
But my favourites would be rather these japanese dramas:
Hello Harinezumi - mystery comedy. It has romance, but it is not main focus
Limit - thriller, survival, psychological
The Werewolf Game: The Beast Side - this is not drama, but series of 8 movies, this one is 2nd in that series and I like it the most. It is about a death game.
And then some others, but they are mostly only comedies or romcoms.