The acting was top-notch. The direction was great: good pacing, not dwelling too much on any one thing, nor overly frenetic jumping from one scene to the next.
The story is great: a good balance of developing the characters, their relationships (and romances); humor (Ron is especially funny); conflict; danger; and of course the climactic battle scene.
The movie definitely assumes that you're well familiar with Harry Potter. This is a good thing: most people who would see this movie would have by now read the books or seen the previous movie. The magic in it is simply part of the story -- it isn't used as a "Gee, wow" gimmick anymore, which would have been boring.