As any review will tell you, Alfonso Cuarón's Harry Potter and the Prisoner of Azkaban, the third adaptation from J.K. Rowling's books about a student wizard, is easily the best movie of the three. It's also probably safe to forecast that it will be the best blockbuster release of the summer. What's harder to get at is why these crowd-pleasing fantasy adventures enter big but recede within a few years to a dim memory of a vaguely good time. I think a major part of the problem has to do with the way movies like Prisoner of Azkaban undershoot the genre of chivalric romance.
In capsule form, the genre of chivalric romance sets its hero-knight on a quest that leads him through a series of (increasingly significant) adventures in which he encounters people who need his help against the forces of evil. What makes those forces evil and what makes the hero-knight good tie in to the romancer's overarching vision of what gives life meaning. (For a more detailed discussion of romance as a genre, read this page of my new book.) In Prisoner of Azkaban the contours of the genre are obscured somewhat because it's a middle section of a series, and because the hero's movements are mostly confined to the grounds of his school. We think of a quest as involving a journey, but here the real "journey" is Harry's growing up, which is fine because in romance the journey--the path, the road, the voyage by water--is symbolic anyway.
Romance is altogether the most richly symbolic of genres, and as a result you can't overstate the importance of its visionary quality. It also supplies an extremely adaptable narrative framework which means it's useful to people whether or not they are visionaries worthy of it. For example, in The Day After Tomorrow, Dennis Quaid is the knight whose quest is to save his son from freezing to death in New York and also to save the planet from ecodisaster. The paternal quest is a complete, symbolic miniature of the larger quest, but that larger quest isn't quite large enough. To have green-liberal concerns take the place of medieval Christianity in chivalric romance is a massive reduction in scope (even if not as empty a reflex as making the Gene Hackman character in The Poseidon Adventure a clergyman).