I know what a wanky thing this is to say but ...
... the book was better.
I know, I know. I hate me too.
But seriously, it's quite a slow paced story for the most part which I think works better in print. Actually, I was surprised when I heard they were making a movie and thought it probably wouldn't work, but it is a pretty good film.
I hate the ending though. It's a cop-out.