Hmm, how to describe this movie. As a stand alone movie, it was okay. A lot of dialog, no action till the end of the movie. Comparing it to the book, it fails miserably. Goblet of fire was a much better movie, and compared to the book better. It is impossible to put the whole book in a single movie, but, at times it felt that they didn't even try.
No quidditch! No watching Ron learn to be keeper, Harry and the twins getting banned for life. There was not a single mention of quidditch.
Levicorpus. The student were using this spell while training in the Room of Requirements. It wasnt mentioned until book 6.
The whole Cho/Harry thing was poorly handled, they made Cho into the person who spilled the beans on the DA group. Also no indication or mention of the coins they used for the meeting purposes. Parts where Ginny glared at Cho was fairly humorous though.
OotP. The whole thing was rushed, no plot development, no nothing. Just basically a group of people fighting death eaters. Not much else was developed.
Harry's nightmares. They showed brief glimpses of it, but at the point when Ron's dad was attacked, they showed nothing of the hospital, Neville's folks. In fact, while they were all in Dumbledore's office, after the dream, Dumbledore sent Harry away with Snape at that moment, claiming we are all in danger.
The attack on McGonagall was not shown, or hinted at. The owl test were only seen in one small moment, and was presided over by Umbridge.
There was a few more I thought maybe should have been included. The acting was superb from Ralph Fiennes ( Voldemort), Alan Rickman ( Snape), and Jason Isaacs ( Lucius Malfoy). The rest of the cast was about par for themselves, nothing outstanding, corny and forced at times. Michael Gambon (Dumbeldore) actually improved a bit in this movie. Previous movies he seems to make the most powerful wizard afraid of the tiniest things.
When seeing this movie, try to forget there is a book about it. It will be a little bit more enjoyable.