While J.K. Rowling's source novels have gotten significantly longer as the series progresses, overflowing with plot, the fifth of the Harry Potter films is twenty minutes shorter than its predecessor. It's a welcome development: as the filmmakers become more comfortable with the material, they seem less beholden to Rowling's work, and more concerned to craft a version of the books that works onscreen.
Inevitably, this means that large swathes of incident from the book are abandoned - Harry's romance is relegated to a footnote - and many smaller set-pieces are entirely omitted. The film feels much more coherent as a consequence, even if it loses perhaps some of the observational character that director Mike Newell brought to the fourth installment. Near the end, the events do seem a little overly compressed - it's hard to understand how the young wizards break in to an apparently well-guarded place so easily, for instance - but for the most part the action moves on coherently.
The key new face this time around is Imelda Staunton, as a new teacher and Ministry of Magic plant; she does a remarkable job of straddling a fine line between menace and high-pitched ridicule, taking what seems like an entirely light-hearted assignment and giving it considerable depth. As the oddball Luna Lovegood, the Irish newcomer Evanna Lynch is excellent, while Helena Bonham-Carter energetically channels the work of her offscreen partner Tim Burton as the blood-curdling Bellatrix Lestrange.
Director David Yates does a particularly good job of marrying the effects work to the live action: while that's presumably also a testament to advances in film technology since the first film, he uses effects in a way that enhances the action rather than distracting from it, and for the most part the effects work seems to belong to the same plane as the real actors, making it that much more convincing.