PoA isn't my favorite HP book, but I think so far it's my favorite movie. CC was so true to the books that I wasn't sure how I would feel about a director who reportedly look more liberties with canon. But PoA flows beautifully, and really makes the pacing of SS and CoS look kind of clunky by comparison. The first two felt like books-turned-movies, whereas PoA feels like a movie that happens to be based on a book. There was only one thing that was left out of the movie that I really missed, which was the explanation of who Prongs, Moony et al were. I mean, I know who they are and all that, but the unintiated will most likely be left wondering. And I'm considerate of them like that ;)
Visually PoA is superior to the other movies, and the FX are lovely. Buckbeak was wonderfully believable, or at least as believable as any half-horse half-eagle can be. The flying over the lake scene put a smile on my face. The dementors were way creepy and the soul-sucking effects gave me the willies.
I could say a lot of other things, but it would all basically come down to the fact that it was really cool :)
And Ron and Hermione are soooo precious!