Goodnight Punpun is a pretty good read. You've probably seen some pictures of it around, it is a pretty popular choice.
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Doubt is a really fun Saw style horror manga. It's also short. read it all, isn't there another one out with a similar style but with birds in the theme? (and another one with a cube where children from school get killed for a game/test)
Lucifer and the Biscuit Hammer is my favorite manga of all time. Not that that means anything. The art takes a little getting used to, but the story is amazing and certain moments make me cry without fail.
i think i've read 5 chapters when i was 18. i probably didn't apreciate it. gonna look minto it again.
Bokurano is a really dark mecha. Very much in the style of Evangelion, but somehow way darker.
lost my interest in that one. :/
Narutaru by the same author. It seems pretty cool and happy at first, but it gets pretty fucking dark and weird by the end.
gonna look into it more, looks and sounds interesting
Akumetsu is basically about why capitalism is the worst.
have read all of it, fitted right into my "sturm und drang" time
Spirit Circle and
Sengoku Youko. gonna look into em after biscuithammer.