
By far my favourite book of the series so far (and likely to remain so, if the movies are representative of the novels), the third book in the Harry Potter series definitely sets the novels going in a direction that I can enjoy. More mature than the previous two books, with a decent plot and twists along the way, there was plenty to enjoy here.
The enriching of the Potter universe was certainly welcomed. Adding layers to the framework established in the first two books and dealing with the story of Harry's parents deaths, the story dealing with betrayal and murder felt a lot more epic than the rather lightweight plots of the previous outings. The addition of macabre elements such as the Dementors and the concept that good guys aren't always that good (in the case of Black, the Dementors, Harry's father, even Harry himself) helped with the maturing tone.
After the ridiculousness of Lockhart in the last book, the calm pleasantness of Lupin and the rage of Sirius Black were far more believable, although the divination teacher Professor Trelawney veered towards being another over-the-top and unsympathetic addition to the book. (Again, it's another of those characters who I felt came across better on-screen than in the novel.) Snape gets some layers too, which is welcome after the cardboard cutout version in the first two books which never seemed to justify his importance in the series.
I'm still not particularly enamored with the character of Harry himself - although he wasn't given everything on a plate in this book and had to actually work at being heroic and making the right decisions. He came off a lot better although, frankly, his and Ron's attitude towards Hermione for most of the book made them look like enormous arseholes to the point where I was hoping that Black would get the little buggers.
The plot's the strong thing here, though. A real page turner and, though once again a deus ex machina pops up at the end to help resolve things, it's not quite as neat or happy as the previous books. The numerous plot threads do weave together nicely, however, and reach a satisfying, if sad, conclusion. Better in plot, better in characterisation, better in twists and worldbuilding, it's certainly a step up from the previous books.
Good stuff.