This is my favorite of the HP novels because I love the backstory of the bad guy. This book and the chapter of the last book with Snape's memories tie up a ton of different threads in the series. I'm still left with the question: it seems that learning non-verbal spells casting would be pretty critical, as demonstrated in Harry's final confrontation with Snape. Why don't they actually learn this?

Also, Slughorn is much more likable in the book than in the movie. The movie presents him as an opportunistic thief (Dentacular leaves). This scene is very different in the book.