I am alone among my friends in liking the Harry Potter movies. I generally find them to be enjoyable and a reasonable approximation of the story in the books.
This one, however, strikes me as being a loose collection of scenes with little in the way of a cohesive thread to unite them. If I hadn't read the book first, I'm pretty sure I would have found myself lost and confused as the story jumped from scene to scene.
For fans of the book, seeing the beautiful renditions of Hogwarts and its students is a real treat. This movie should really be considered a series of sketches depicting scenes from the book (and some that don't exist in the book at all), instead of a cohesive plot that mirrors the novel.