I don't want to go on and on, so let's get to the point: read the book. Don't see the movie. Unless it's free.
The book will change something in you, stir something. It is real, gritty, unpleasant, depressing, raw, and joyful. The movie is a weak attempt at recreating those feelings, while falling very short of the mark in the aspects of character development and plot elements that really make the book (though some of them are awful or sad things, they are what make it great...). I have a pure love for this book, and I'm thankful to my Dad for shipping it to me. I feel irritated that I spent $13 and an afternoon wasted on the movie.