Liar Game
One of the best psychological mangas out there. Akiyama is seriously one of the smartest protagonists in the world of manga. The beginning portion had more interesting games, the end is a little meh, and leaves a lot of open questions, unfortunately. But worth several read-throughs for sure.
Death Note
The art is fantastic, and the story is good until when L is killed. After that, it goes severely downhill. So many plot holes and there's no one to root for by the end of the manga. Seems like they ran out of ideas by the second half. All the so-called geniuses are pretty dumb in the end, what a let down.
Bastard (hwang Youngchan)
One of the best dark thriller webtoons out there. It keeps you on the edge of your seat. Everyone is twisted, but you want to root for the protagonist. It's worth re-reading after the first read-through!
Hogu Hagyeongsu
Very good dark BL, comparable to Killing Stalking. Art is really good, and the plot is overall well-paced. It has lots of mature themes, so may not be right for everyone. This webtoon is the closest to Killing Stalking in terms of dark BL genre, although Killing Stalking is still superior.
Unfather
The art is so-so, the protagonist is well drawn and beautiful, but everyone else is average or ugly. The plot is dark, but not as dark as I would have liked. None of the characters are likeable and they're all twisted, which I liked about this webtoon. It's hard to sympathize with any of these characters, and it wasn't surprising that they all ended up unhappy and trapped in their futures.
Obey Me
It's quite dark, a BL in the same vein as Killing Stalking. Personally, it's not as dark as I would have liked though. I think the plot is a little weird in pacing and there are some gaps in the story, but it was overall a good read. I'm not surprised at all at the ending.
Killing Stalking
Classic dark BL, it's very well written and the art is gorgeous. It deals with a lot of mature themes, so may not be appropriate for people who don't like this kind of material. Ending was tragic, but made sense as none of these characters deserved a happy ending.
Brawling Go