Without babbling too much, this is a cool comic; generally speaking if you prefer indie graphic novels over mainstream superhero comics then chances are you will probably enjoy this. Its witty, cynical, poignant even and full of enough pop culture references to encourage you to listen to your old albums. The artwork is very tasteful; monochrome with realistically drawn people with slightly simplified features (think Ghost World and the like) which works very with the storyline.
That said, all the previous reviewers are correct, it's odd. At first you think it'll be a straightforward "protagonist enters setting, cue monologue" which it is, but it flips very quickly and can be tricky to follow. I feel the need to state that this is indeed a book about magic and people who practice it, I found it at times hard to tell if Gillen was using magic as a metaphor or even just as a colloquialism, but turned out he really did mean good ol voodoo witchcraft.
Either way, its worth a read.