Firstly I'll say that I enjoyed it. With that out of the way, the film HEAVILY embellishes the book. What was once a footnote becomes a whole scene, and this is how Jackson plans to stretch out a single book into three films. That's not a bad thing. I never felt the book actually went into any massive amount of detail describing what was going on. Your imagination kinda filled in the blanks (part of the charm of reading in the first place.) Film adaptations are just that. Adaptations. This is just one way to imagine the story.
Now I'll play devil's advocate, and suggest this might be part of the trend studios are following to milk a franchise for all it's worth, like it did with splitting up the last Potter and Twilight books into two movies. Personally though, after watching the film, I can't think of anything I would have trimmed out.