Although the book always carries much more detail it brings the pace of reading to a halt. The movie captures the essence of the plot and changed the timing of a few scenes, like when Bella skips school and rides on Jacob's bike to La Push. You never really miss anything important though and the movie is sooo much more fun, fast-paced, and absolutely excellent!
This is by far the best Harry Potter movie yet... still can't wait for the first of two movies based on Book 7. BUT as an avid HP book lover, there was a lot of missing details, even whole sections were cut or simplified. The book is called the Half Blood Prince, so the development of how we learn of this "prince" ties everything together, in the movie it didn't occur this way and left me wonderig what will be cut in the last film. Overall, this film was amazingly hilarious, witty, well-crafted.... it made me laugh, cry, cringe with fear - in short it contained everything a great movie should contain.