I tend to think the book is always better than the movie, so I am biased but...
I think the book does a better job of letting the reader or audience know about the characters in a deeper way. In the movie there just isn't enough time to build up things as slowly and as clearly as you can in a book. That to me was probably the biggest factor in liking the book more than the movie.
Needless to say, the book was a thousand times better than the movie. The movie did try to portray most of the important parts of the novel, but the plot moved along a bit too quickly, leaving a large part of the story unexplained or untouched, and I believe that greatly altered the story as a whole. Frankly speaking, if I had seen the movie before reading the book, I'm sure I would have been constantly asking myself, "What's going on? Why is he-?"