For a book that is the second to last in the series, this one does a lot of things right. Order of the Phoenix, in my opinion, did many things wrong. First of all, this novel focuses on three vital things: Snape. I mean, the book is named after him. We learn a bit about him and the book Harry finds in the potions classroom, which he uses to his advantage. Next is Draco Malfoy. After his father, Lucius Malfoy, failed to deliver the prophecy to Lord Voldemort, he was sent to Azkaban. Voldemort was furious with Lucius, so as a result, he assigns Draco the most difficult assignment: to kill Albus Dumbledore. Throughout the novel, Draco gets a lot of character development. Yes, he is a Slytherin and Harry's bully, but he wouldn't go as far as killing someone, especially someone as powerful as the headmaster. And finally, Tom Riddle, aka Lord Voldemort. During his sixth year, Harry received special lessons from Dumbledore. Dumbledore shows Harry the memories he has collected regarding Voldemort's past and rise to power: his heritage, his birth, his first meeting with Dumbledore, his path to immortality, etc.
Those three plot points are what make the novel enjoyable, and I had a blast reading this. Unfortunately, the movie adaptation screwed up big time. It cut so much of Voldemort's memories, which deeply upset me. It also focused less on the major plot points and more on the extra stuff that was briefly mentioned in the book.
Putting that aside, this was a fantastic read and perfectly sets up the events in the final book.