I fell in love with this book the moment I turned the last page. It is my favorite of the entire series, and in my top 5 fantasy books as well.
Harry returns for his third year at Hogwarts, in the shadow of an escaped mass murderer and the scary Dementors. Sirius Black, Voldemort's right-hand man, has escaped the supposedly inescapable fortress of Azkaban and is baying for Harry's blood. But life at Hogwarts goes on, despite everything. Disappointment on the Quidditch field, the best Defence against Dark Arts classes he's had yet, a couple of new subjects, Harry's hands are full. But then he learns an earth-shattering secret, a secret that will change his life forever.
I have lost count of the number of times I have read The Prisoner of Azkaban. The series takes a darker turn with this book, with Harry and his friends maturing and learning that good always doesn't win. This book doesn't have a happy ending like the two previous ones, setting the tone for the ones to come. The Dementors are probably Rowling's most inspired creation in the entire series. The idea of a faceless fiend who can suck all joy out of you with its mere presence is chilling. Of course, there is some fun, but the darkness and edginess play a more prominent role. You are on the edge of your seat most of the time, and the twist ending makes it all the more memorable.
I think this book sort of sets the foundation for the entire series. It is from this book that events accelerate, the Dark forces get a boost. Voldemort does not make an appearance in this book, but that somehow adds to the danger. Also, the relationships between James, Lily, Sirius, Lupin and Snape are established, relationships that are crucial to the plot of this and later stories. A fantastic story, it's probably the most thumbed book on my bookshelf.
Which is your favorite Potter book? What do you like about it?