Before I begin, let me say that I will NOT spoil any part of the movie by giving details. I'm sure most rabid fans have already seen the film, but for the sake of those who may be swayed to see it, I won't give away the details.
It was two an a half hours long, I'm sure there was a lot of trimming involved in the transition between the book and the movie. The movie seemed to hang together rather well. If it were a weight lifter, I'd say the movie had all the muscle it needed, with just enough fat to give it character.
It was by far not a minimalist movie. There were plenty of special effects, the plot carried through nicely, and the mysteries in the story actually stayed mysterious until they were solved. I can say this because of two things.
First, I'm not completely clueless, so a thin plot with badly presented secrets would have turned me off. Second, I have yet to actually read a Harry Potter book, which makes the movies completely new experiences, rather than exercises in comparative storytelling via disparate media.
An interesting bit to the film, is that Harry does not reveal all his findings to Dumbledor. Perhaps he may tell Sirius Black the detail he failed to mention, at a later time (in another movie?), but there is at least one major discovery that he keeps close to his vest.
Not having seen the previous movie, The Prisoner of Azkhaban, I'm not sure if this is due to time constraints, or if it has something to do with Harry's evolving personality. None-the-less The movie is quite enjoyable with plenty of twists. Even little things at the beginning that seem trivial or cliché actually amount to something through the course of the film.