* AlwaysChaoticEvil: His villains. A common complaint about Ennis' works is the man is nearly unable to write villains that are not [[CompleteMonster Complete Monsters]] and are so horrible that it gets really boring fast from work to work. It comes off like he uses stock villains just to get his [[AuthorTract Author Tracts]] across to the reader.
** According to Ennis himself, this is a direct reaction to the concept of "JokerImmunity" that pervades the medium. He once phrased it in a ''Wizard'' interview as writing villains who are "worth the bullet"; he doesn't enjoy works in which the hero proves his moral superiority by letting the villain live, as that's usually a choice on the hero's part that will get someone else killed at some point down the road.
*** Of course, this doesn't discount the trope in that his villains end up coming out one-dimensional and poorly written.
* CrossesTheLineTwice: Ennis has an extraordinarily dark sense of humor and a penchant for sex jokes, which turns many would-be readers off from his work. While he's not unusual in that regard among other UK-based writers (Warren Ellis in particular can give him a run for his money), Ennis is the one who's built a reputation off of it.