DC's Identity Crisis is IMO one of the best graphic novel of all time. it's not a superhero adventure but a superhero tragedy. I think it really is a must read!
if your looking for a manga with the story and depth of a graphic novel you should try reading Katsuhiro Otomo's Akira
Preacher, by Garth Ennis.
Kenichi History's Strongest Disciple
batman: long Halloween