Just saw Harry Potter 3 at the movie theater. Harry Potter and the Prisoner of Azkaban is my favourite of all the Harry Potter books, and the movie disappointed me in that regard. When I read the book, there were a lot of "aha" moments when mysteries from the first two books were explained. The movie did not give me that feeling at all. But then I know the story already by the time I watched the movie, so I guess that's unfair.
One thing held up to my expectations though -- Professor Lupin. He was as amiable as the one portraited in the book :)