The Movie hit all the important plot points of the book. It took out what wasn't needed for the story to continue, but the flow wasn't there because of this, they took alot of info and shoved it at the audience. If you haven't read the book, a lot of the "why is this happening" can go over your head.
The flash backs are the best examples of this.
Other than that, The action was extremely well done, They kept it real, but made sure not to focus on the death scenes.
Over all the movie was right up there with the best, and the directors can learn from the mistakes made in this one and correct them in the next.