This cover is just dreadfully embarrassing, and if this had been available in Australia on Kindle I would have bought it purely to avoid carrying this awful cover around. It looks like the worst sort of trashy urban fantasy, and while it's not quite that, it's really not great.
Discount Armageddon is the sort of urban fantasy that has a heroine that makes sarcastic quips all the time, which drives me a bit crazy. I mean, you have apparently been raised to be a hunter of monsters, vigorously trained from a young age, you're risking death, we're inside your head in a first person narrative, and you're quipping. Does nothing affect you emotionally? Oh, apart from that man who hates you and all you stand for and whom you basically fall in lust with at first sight. I guess you probably knew how fast he was going to change his mind about all that stuff.
I'm making this sound much more irritating than it was - I did quite enjoy reading it, it was fun and fast paced and light hearted, but it did suffer from being quite silly, and I couldn't get over some of the sillier things. On the plus side, I like the idea of the world being filled with a vast variety of crazy monsters (cryptids), and I enjoyed the story of Discount Armageddon - but it's probably the weakest book of McGuire's I've read.