I liked the book a lot, but I didn't think the movie adapted it as well as it should have.
For one thing, I don't like the color palate at all. Everything has a drab blue/grey tint. I think the vivid colors of the first two movies are much more fitting. PoA (the book) is a little darker than the first two in some ways, but overall it's still a fun children's story. I think it was a poor choice to make that figurative darkness literal.
Come to think of it, the whole feel of the movie (not just the colors) is darker than I think it should be. The book was a bit more serious than the first two, but the movie almost feels as if it's a Gothic horror film rather than a kids' movie with dark elements.
I also don't like that the kids are never seen in their Hogwarts uniforms in the whole movie. It takes away a bit of the British-ness of the series.
They never properly explained that the Marauders were all Animagi, that thy studied to become so because Lupin was a werewolf, and the significance of the nicknames. If you watch the later movies without having read the books, it gets really weird when people start calling Sirius "Padfoot" for no apparent reason.
They also mostly omitted the Firebolt subplot. It's a short movie compared to most of the others, so they definitely had time to include it. Doing so would've done a lot more to emphasize the bond between Harry an Sirius than having that scene come almost out of nowhere at the end.
I also dislike that they changed the Hogwarts grounds and Flitwick's appearance. It creates an annoying discontinuity with the first two movies that really wasn't necessary.
I could go on, but you get the picture. XD It's not a bad movie or anything; it just did more to annoy me than most of the others.
I dunno. The foreshadowing with the clock tower was good, but I though some of the scene transitions, like the one where the Whomping Willow kills a bird, were kind of pointless. Apart from those and maybe a couple of other things, the direction didn't really stand out to me.