Constantine came from a comic series called Hellblazer, which was a spinoff of the Swamp Thing comic series (in the pages of which John Constantine debuted).
Ron can answer for himself, but you mention Superman Returns and that illustrates (for me) how one could not like a particular movie and still enjoy the subject matter enough to hold out hope for future entries. I would probably put Iron Man as the top comic movie for me, possibly followed by the Dark Knight and the second Spider-Man. I liked the first X-Men, but not so much the second. I didn't bother with 3 or Wolverine Origins.
Others you might not suspect are adaptations of comic books:
Ghost World
Surrogates
30 Days of Night
Okay, I can't think of any more. But, there are quite a few that have the potential to surprise. I didn't know Surrogates was a comic book adaptation until after it was released.