I have a complicated reaction to it. If you enjoy zombie movies and books, it's sort of a vicious counter to them, but the titular monsters aren't anywhere near as scary as Ennis wants you to think they are, particularly since most of the book is set months after the initial outbreak. It's got grace notes to it, but honestly, it's one of the weakest things Ennis has ever written.
Also, the first issue contains probably one of the goriest, most actively repulsive scenes in Ennis's output to date.