Of course, the story tracks the career of a young man, David Valentine, who belongs to the resistance movement. Certain areas of the North American continent are largely free of vampire incursion, and serve as "at seige" nations of sorts, and David Valentine is a soldier for this group. The aliens themselves are at war; the vampires being those who became addicted to siphoning off "aura" from other beings (via drinking their blood) and those who don't. These less vampiric aliens brought a few key advantages to struggling humanity; the ability to unlock latent mental and physical abilities. David Valentine is a "wolf"---his senses, reflexes and stamina are greatly increases from his human normative pre-wolf days, making him a superhuman warrior... although still not exactly a match for a vampire one on one by a long shot.
Knight is a pretty good writer; he makes David a believable and interesting character, he describes a fantastic setting, and he manages to keep tension and plot structure at a nice clip. I found the book very easy to read through in a short period of time (of course, it's also not that long of a book; just shy of 400 pages in mass market paperback.) As well as the fascinating secret history aspect of the books, there's a lot of implicit setting stuff that I found really intriguing.
For instance, the remainder of the US has been knocked back into a technological Dark Age of sorts; kinda like the early 1800s. Knight also had society resemble the early 1800s, which is one of the things I found more interesting; small rural towns and the lifestyle of early American pioneers... but with the constand fear of vampire attacks.
This also comes at an especially opportune time, as I'm in the middle of developing my vampire kingdom module for my modular campaign setting, and this is a good model of vampire kingdoms ruled by various vampires, or "Kurian lords" as they're called here. Knight himself says that he first developed this setting as a roleplaying game setting, and ran games there for his friends.
Anyway... check it out. A fun new take on a classic idea.