I think after I felt so let down by GoF, I was expecting worse, so I was sooo relieved when I enjoyed this movie so much. It is definitely better than the last two, but I still love the magic of the first 2 films. I understand thought that OotP is a much darker book, and I think they managed this without making it depressing.
I don't think there were too many vital parts missed out, the only thing I think could have been done much better is the fight in the ministry of magic. Where was the room with the brains, the room with the revolving floor, and the death eater who turned into a baby. And I did miss the bit where Harry trashes Dumbledore's office, as this is so emotional in the book.
Evanna Lynch IS Luna, she couldn't have been better, but Tonks wasn't as I imagined her, I'm sure she has short hair in the book. Gary Oldman was brilliant, but I expected to be much more upset when he died and for some reason I wasn't.
Overall though it was a great film and I really enjoyed watching it. It was that good I'm going to see it again tomorrow night. See it as soon as possible!!! (but I do wish there was more Malfoy)