If you liked 20th century boys i recommend "Monster" and "Pluto", monsters from the same author and i think Pluto is too, both of them are very good. And if you havent read the sequel to 20th Century boys (i doubt you havent), read 21st Century Boys too.
Also try Vinland Saga, Eden:Its an Endless world, Zetman, DeadMan Wonderland, and Holyland. Their all Seinen (except maybe for Deadman Wonderland), good, all that stuff you said too.
Hmmm, this ones Shounen, but also suggest you read Psyren.
(also, this ones Korean (so it reaRAB left to right) and has the shabiest/badest looking art ive ever seen, but read Ares, trust me.....)
