I thought the movie was very good. I was expecting them to have to miss out so much due to the sheer length of the book, but I think they actually managed to get all of the important parts in. Just occasionally in these films, I think there is something that's done better than in the book; in this case, I think Neville being the one to tell Harry what happened to his parents has a lot more impact than Dumbledore blabbing all of Neville's business to him (as he does in the book).
My one major gripe is the way the discovery of the DA by Umbridge was handled. In the film, Snape has been giving Veritaserum to Umbridge in order to interrogate all of the students. And it's real. In the book, he's giving it to her only for Harry - and of course, it isn't real, Snape wouldn't give her real Veritaserum. It's the betrayal that's real. In the book, they are betrayed by Cho's friend Marietta (like no one saw that coming). I quite understand why they spliced her character with Cho's in the film, but the whole Veritaserum thing both cheapens it and brings Snape across all wrong.
I also thought Luna was very good. Everything about her is testament to her looniness, and Rowling usually describes her as looking “dreamy” or “faraway”. There wasn't a lot of room for her to talk about conspiracies and such in the film, which didn't bother me - but I do hope that the subsequent films will leave room for the development she needs.