Loved the book, hated the movie. And, the reason I usually do not watch the book-based movies, especially before I read the book is exactly this - they changed so many things in the movie, and I mean essential things, that you can see a resemblance, but that's that. Nothing more.
Even if you did see the movie, you should read this. Just so you know what you've missed. It's not the best book ever, but compared to that sorry excuse for a movie, it's a damn classic.