This book definitely keeps you guessing - a bit like James Barclay in the way that the author doesn't flinch at killing off characters - you know the type, "the six heroes battled their way through two hundred slavering monsters using their barely trained but stupendous powers, with barely a scratch, and the hero and heroine march off into the sunset and live happily ever after", blech!
You get the sense of isolation and remoteness, the fact that people are fighting for their survival after decades of occupation by a race of beings that are superior predators. The invaders can create monsters to do their bidding, sending them out to harvest human souls to preserve their lives indefinitely - hence the vampire bit. However, that's where the similarity to most vampire stories ends - forget snuggling up to a sexy vampire and getting lost in ecstacy and all that rubbish - these vampires will rampage through whole villages and rip everyone's heart out, sending the unfortunates' souls back to their master to feed on.
It's not that gruesomely detailed, really, but the reactions and emotions of the humans are understandable given the force they face. David Valentine is orphaned by a patrol (human helpers of the invaders - lots of layers to this, but think nazi collaborators in WWII) and joins the resistance force as a wolf (there are also cats - lone assassins - and bears - elite, baddest human fighters).
As I said, this book is anything but predictable, the characters very well fleshed out and, wonder of wonders, not everything is expained in two-year old diction at the start of the book, the reader is credited with some intelligence to come to our own conclusions, and all through the story, new complexities are added to the plot. All in all, having read a lot of fantasy books, I rate this very highly - actually, i've just ordered the rest of the series!