In the various musing on it that I have done, I realized that it is perfect for the "Folklore" category of Once Upon a Time Challenge and I'm shocked that I didn't see it at first. That's the thing about a book like this, though. It is so layered it takes months to peel away at it; and the more I peel, the more I find.
Folklore takes the customs of a group of people and tells it in story form, usually (to my layman's mind) using a lot of exaggeration and showing that particular people to be something special. Think of the Jack tales, if you will.
Snyder and King (especially in King's half of the novel) have taken the vampire legend and made it something completely American, indigenous only to this breed of people. In short, they've created a new folklore.
If you like vampire stories, or the Wild West, or revengeful women, or. .. heck, just as long as you like to read but don't mind a little gore (okay, even if you DON'T like to read; this might be a good starting point), give this one a try. Let it marinate for a while afterwards and see where it takes you.
Darn fine book.