This book has to be the most masterfully written of the series. J.K. sounds like she's really in a very comfortable, easy place in her life, and it's showing through her improved writing. Up until the last fifty pages, the book is excellent, definitely the best of the series, and then in the next fifty, it's like the book has been set on fast-forward, rushing through events. Now I understand that she didn't want to make this thing 2000 pages long, but it feels very odd for her to switch from very calculated, precise writing to her usual fast-paced, smaller book style. I understand that she would have wanted to spend as little time as possible dwelling on Sirius's death, but the ending feels as though she simply ended it for the sake of a break. It has to be one of the weakest endings, but as far as the rest of the book goes, it's the best, which makes it my second favorite:
1) Prisoner of Azkaban
2) Order of the Phoenix
3) Goblet of Fire
4) Philosopher's Stone
5) Chamber of Secrets