If you think Preacher's shocking, avoid his biggest inspiration on that, Cormac McCarthy. ;)
And he is probably the best writer of war stories since Archie Goodwin. He has an amazingly even hand when writing about soldiers, on all sides. And the empathy he creates for the soldiers' and sailors' situations is unparalleled; Garth Ennis, whatever you may say(and I personally don't care about his shock content, because I don't find it that shocking and sometimes even find it funny in a YOUNG ONES way, like the latest descendant of Jesus" "Humperdidoo!"), has a really good handle on characterization. It also does seem however, that the stories prove he doesn't really have the need of shock content for his stories to work. Even when he's trying to be funny while in "serious" mode, like "Archangel,"(I think--the one about the poor bastard piloting the camship) he still works well and reveals a great deal of subtlety. And a very strong moral sense based on real life, not ideals.
Which makes me think that he's not trying to shock in the other stuff: I believe he just likes writing that way, that he gets a kick out of it. And I don't have a problem with that.
For the record, my two favorites from WAR STORY were the amazing, beautiful and tragic "Nightingale"(especially given Lloyd's art) and "Condors," because while it's very talky, I enjoy it.