I wish they wouldn't add things out of the blue (such as the unexpected fate of the burrow) or change things outright (like the appearance of the great hall). And Lavender, while funny, was not at all what I'd pictured.
Overall, though, I was quite pleased. The director did a good job balancing Draco's torment with Ron's brilliant physical humor, and the friendship bond between Harry and Hermione is cemented even more strongly. Snape is deliciously evil (or is he?) and sweet-hearted Luna is just as lovably daft as expected.