(Spoilers ahead. You have been warned.)
The Good: With regards to the tangible changes to the movie (the new geography of Hogwarts, the costumes, and the special effects) this movie receives excellent marks. I heartily agree with the assumption that since Harry, Ron, and Hermione are growing up, then so must their movies. The new clock tower to the campus is spooky, and will most certainly help in future films. The costumes are not as drastic as I had thought, and I must say that both the Dementors and Buckbeak the Hippogriff looked very good on screen, and are pretty much what I had envisioned from the books. While some have complained about the Dementors' "soul-sucking" effect, I found it a very good visual representation from the books. It was also nice to finally see the Marauder's Map on screen, and it was close to what I had envisioned from the books.
The Bad: Sadly, it is with the deletions of material from the book to the movie that I must give failing marks. While the film focuses mainly on the issue of Harry's maturity into adolescence, I felt that at some points, perhaps TOO MUCH focus was on Harry. Also, some much needed exposition was necessary to answer various questions. For example: Black, Lupin, Pettigrew, Harry's parents (James and Lily) and Snape all knew each other because they were classmates at Hogwarts. The problem is that only those who had read the books beforehand would know that, and truly appreciate the scene in the Shrieking Shack, where Pettigrew is revealed. Another problem for changing something mid-way: Since these movies are supposed to complement each other, then the changes made here will have to be carried on in future films. And with regards to the argument about eliminating the back story of the Marauder's map, with the intent of revealing that information in future movies... Well, what if it isn't?
A personal comment: I must say that the "Lord of the Rings" movies did a much better job of explaining character relationships for fans and non-fans of the books they were based on.
Overall: Despite its inherent flaws, I must say that I found this movie entertaining. This film was made with fans of the books in mind, and it would be remiss of me not to stress that you should read the book beforehand to appreciate what you will see on screen.