Having read the book, I can say that they really butchered this movie by taking out far too much of the original story. As a result you get a story that feels rushed and incomplete. (Not to mention that to save time they took some serious liberties with the story.) It should be noted that the movie is only about the first half of the book, and even that part of it is much different in the book.
I really think that this should have been a TV series, where they could explore it all in depth over time. Each episode could have exposed a bit more, and they could have gotten four or 5 seasons out of it.
Instead you have a movie that is not awful, but it's not that good either. I'd suggest it as something to pick up on the cheap after having read the book. That way you can get a taste of how this would have played out had they followed the book more closely.