It's hard to describe this book in more detail than what's on the cover blurb without giving spoilers. In theory, it's a post-apocalyptic science fiction/adventure story, but it's really about friendship, loyalty, doing the right thing, and ninjas.
This is one of those books where it's the way it's written that is more entertaining than the story itself. The style may or may not be to your liking, as the first-person narrator goes off on many, many tangents. Witticisms and inventive euphemisms abound. None of it is strictly necessary for the story -- if you just want a rollicking adventure, this book takes a while to get there, and the adventure is buried beneath a lot of wordy prose that at times begins to sound like the author is just trying to impress you with his cleverness.
However, it is clever and funny, and if style is important to you, this is a stylish novel. And there are some great characters. And ninjas.