Somewhat entertaining at it's best but mostly disappointing

Rating: 5/10 (12 December 2012)

I will start by voicing my initial disappointment when I first saw the film in the movie theater in 2004. I was so disappointed I've avoided watching it again until recently. I had hoped I'd like it better the second time but sadly I did not.
Had I not cared about the books I would have probably enjoyed the movie more than I actually did and here are my reasons: I did not understand the pressing need the director seemingly felt to twist every little scene in the book. From small unimportant details like Harry's ride on Buckbeak to the importance of Crookshanks being left out (and the Whooping Willow going from whipping it's branches madly to quietness without any explanation). Not one scene followed the book with precision.
Scenes were made up specifically for the movie: The part when Hermione throws a stone at Harry's head while hidden outside of Hagrid's hut. Ron being fully awake when Harry and Hermione use the time-turner. Harry casting a spell under his sheets (Lumos Maxima) which contradicts the rule that underage wizards are forbidden to do magic outside of school - a detail that should have been explained in more detail as it becomes important in later books (although the scene was amusing as most scenes with Uncle Vernon are). Sirius' soul levitating out of his mouth during the Dementor scene.
And what's with the talking heads hanging in the Knight Bus?! They are not funny, they do not bring anything to the film, they are NOT in the books! They do not even fit the scene!
Harry receiving the Firebolt at Christmas was cut out and so was the fight that the happening originated. The crackling tension between Ron and Hermione over their pets and the subsequent fight ditto. The relationship between Lupin and Sirius was badly explained and his knowing about the Map of Marauders was not explained at all. The (very important) mention of who were really Padfoot, Mooney, Wormtail and Prongs was not made even though it plays an important role when it comes to understanding who these men that Harry barely knows once where.
I found Hogwarts' change of scenery disappointing as the grounds were not recognizable and seeing that this movie is a follow up of two previous ones, it was completely unnecessary. The fact that students mostly walk around in regular clothing was a bit disappointing as well.
In conclusion, lots of important scenes were left out or replaced by happenings that were seemingly made up by the director himself, distancing the movie from the original story.
Not all was bad about it however: the background music was lovely even though it lacked some magic; the first scenes were okay and the first appearance of a Dementor was as creepy as I imagined it to be. The scenes are breathtaking, Buckbeak was beautifully made as was the scene in which Harry flies on him (even though it was completely unnecessary for the plot and honestly a waste of movie space), the Boggart scene was amusing. I'm positive I would have enjoyed the movie hadn't I been so utterly miffed over it's deviation from the book.