I saw this movie with my 14 and 16 year olds, and we all had a good time. This movie isn't Up; it's not that serious. It's just a lot of fun for 90 minutes, and doesn't pretend to be anything but that. The animation is good enough that you forget about it being animated.
If you're not familiar with the Harry Potter books, you'll find the plot a bit hard to follow. If you are familiar with the books, you'll find they took out too much in condensing the book into a movie, made the lake scene less scary (and less effective), and didn't fully develop the emotion that helps the book be so effective. The only actor who really gets to stretch his legs is the one who plays Malfoy, and he does a great job. The director also chose to insert scenes to give the villians a little more face time, that weren't in the book at all. Overall, it's a decent, entertaining film, but not as good as some of the previous efforts.