Thanks for the suggestions everyone, unfortunately I've already read everything you had listed 101010, though GUNMM and Gantz are two old favorites (same with Black Lagoon). I also significantly preferred the manga of Shiki to the anime, I thought the striking art style was better suited to stills.
I agree exactly Nolzi, Dorohedoro was such an excellent example of " "mature" " storytelling and deep characters. If you haven't read Keyman you definitely should, it's by far the closest thing to Dorohedoro that I've read, and if you're just looking for strong storytelling in general you should check out anything by Kitoh Moriho, Ashinano Hitoshi, or Mizukami Satoshi. Though Satoshi might be a bit too fantasy or black/white I still think he writes really interesting characters and conflicts. Anyway, I'll be sure to to check out Freaks' Squeele and get back to you on it this week.