I recommend the Spiderman manga, your warning be damned. The writer clearly didn't want to write generic superhero stories, and the series gets darker and darker until Marvel cancelled it because it couldn't really be sold anymore. The artist went on to Crying Freeman, so that's a good example of the kind of direction it was aiming towards. It's a really interesting read of a series that's desperately straining at the limits of "how fucked up can I make this hero".
Also if you like manga batman, it's worth watching the Batman TBATB tribute episode to it. It's a really loving parody of old anime superheros.