Awesome movie, but like everyone has said there is a lot missing that was in the book. I guess when you're trying to fit it into a certain length film something has to be sacrificed. Lord of the Rings springs to mind, even though the extended edition was over 3 hours long, I noticed certain things missing. That said I've read the books like 100 times already, so no surprise that it was easy to pick up. I suppose it's where you draw the line that's debatable.
All in all though, I loved this, not my favourite HP movie, but certainly up there.