Let me start by saying that this book is very much unlike Carey's other books and to be able to pull of such a change of voice is a credit to her writing skill.
This is a rare book with vivid characters and a wonderful deeply emotional story. What I liked very much was that that Carey seems to make it a point that there's no black & white. There's no traditional villain, no one is all evil or all good, the story is driven by other things. It's a story of personal survival and it's also a case study of how life would be if you couldn't feel fear. In that sense it's almost philosophical, even if I wished it had been fleshed out more.
Either way, it's one of those rare books that linger in your mind long after you read them. Enjoy, it's well worth it.