It seems that people in Chicago were handed tickets to their very own private showing of Harry Potter and the Prisoner of Azkaban last Sunday and Ain't It Cool News has a review. Please be aware of the profanity content on this site.
You can read the review here (at your own risk) but here are a few lines to wet your appetite.
The movie is a huge improvement over the first two HP films. It is rich, deep, and dynamic. Director Alfonso Cuaron really knows how to use the camera. The camera is constantly in motion, and there are dramatic and some times extreme angles; but it's not jarring or excessive, everything flows together beautifully. In the earlier HP movies there was a lot of pedestrian 'coverage' which is often the result of multiple-camera shooting to economize on time. This might have had to do with the child actors only being available for limited hours. Perhaps now that they're older, they can work longer days, and Cuaron benefitted from that. In any case, the swirling camera and imaginative angles let you see the world of Hogwarts in something close to 360' and this makes it seem much bigger, and more real, than in the prior movies.
The effects which were finished or near looked quite good. My 7-y-o son was particularly impressed by the 'Dementors' which are black-clad, ghostly prison guards. Their horrifying specialty is 'soul-sucking,' and when they are near it gets cold; there's a neat scene early on where their approach is forewarned by ice spreading across a window and into a nearby bottle. A smaller effect we particularly liked was the 'textbook' for Care of Magical Creatures class, which has teeth, claws, and is prone to bite, unless it's sleeping where all monsters sleep--under the bed! There's a Hippogriff creature ('Buckbeak') which was nearly done in some scenes and looked great, in others was only partially done, in some not far from a wireframe, which was actually quite interesting.
Read the rest of the review at your own risk and thanks to Emanuelle and Casey for the tip.