Haven't watch that many, and we may have different taste. Thriller and mystery aside, I kinda love psychological drama. You can check their synopsis or trailer first. For me, these dramas are interesting:
99.9 Criminal Lawyer (has S2 but I rated it lower so maybe it gets a bit worse, there's a bit of comedy)
A Suffocatingly Lonely Death
Don't Call It Mystery (it's dark comedy mystery, has specials and movie, both worth to watch especially so the specials)
Himitsu: The Top Secret (slight romance, some kisses)
Hoshi Shinichi no Fushigina Fushigina Tanpen Dorama
Human Vapor
Naoki Hanzawa (has S2 but I haven't watch it)
Quartet (there's like love pentagon there, but romance is never the main focus just to set the dynamic between the characters)
Reboot (romance is there but more like family love rather than romantic love with skinship, there's hugs but no kisses)
Shiawase Kanako no Koroshiya Seikatsu (dark comedy action, slight romance in S1, has ongoing S2, seems like it's a bit hard to find it. There's 4/5 episodes already airing yet I still could only find 3 eps)
The Last Man: The Blind Profiler (there's a bit of comedy here and there, has movie but I haven't find it yet)
Unnatural
Celebrity 
