The book is so very much different from the film. Obviously you'll find that out tho. Just so you're not totally shocked.
I read the book after seeing the movie and it added an entirely new dimension to the world I'd already seen depicted in the film. It's like each compliments each other very nicely. I liked everything about the movie but once read the book the whole thing really took off (in my mind anyway)
But you'll have a totally different experience. Just please...don't expect the book in film form. Most of the people I know that have also read the book hold that as the biggest fault of the movie. Very loosely based.