Generally faithful adaptation but extremely disjointed. Too many unessential scenes adapted from the book as fan service, yet nearly incomprehensible as a stand-alone movie. Case in point: In the end, Snape reveals he's the "Half-Blood Prince"-- with no explanation that his father is a Muggle and his mother's last name was Prince. The only way this revelation would have meaning is if you read the book.
It had its moments, but I think I liked this Potter film the least.
My current ranking of movies is as follows:
- Goblet of Fire
- Prisoner of Azkaban
- Chamber of Secrets
- Sorcerer's Stone
- Order of the Phoenix
- Half-Blood Prince