Harry Potter and the Prisoner of Azkaban is a great film. We saw it yesterday and really enjoyed it. I'll spare the re-hash of most of the reviews I've read, but the film was much more "grown-up" than the previous two (which works well with the books' unfolding of themes). Director Alfonso Cuaron did a great job with his telling of the story. I also liked the visuals. The Marauder's Map was done very well, and the dementors were pretty creepy. In fact, the overall effects have progressively improved. We re-watched Sorceror's Stone this weekend (in anticipation!), and although I thought it was well done, there were a few points where substandard visual effects distracted from the movie. (I'm thinking specifically of Firenze and of the cloaked Quirell/Voldemort in the Dark Forest.) I've also liked how they've maintained a consistent cast throughout the films (minus Dumbledore, of course, and a few minor folks).
But that leads to one nagging (minor) question: What happened to Crabbe? He's on-screen a few times at the front end of POA, but later on, everytime we see Malfoy, he's flanked by Goyle and some no-name Slytherin.
Obviously, that's a pretty small criticism. Otherwise, I probably would have enjoyed the addition of some extra stuff from the book (hey, I did the LotR marathon in one day!), but I don't think the exclusions detracted from the movie. I plan on seeing it again. Soon.