Harry Potter and the Half-Blood Prince

Actually, it's really my favorite I think ! I don't know why but I really like how the feeling are treated in the book. I mean, of course, how the (love) relationships are explained. Everything is not black and white, and seeing the multiples jalousies add something more. Rowling managed to describe perfectly this “creature” of love inside everybody. And, of course, the main story is so great. For once, Harry had the right intuition, it's so funny to read how he wants to demonstrate he's right !
And every time I read it, I can't stand the secrecy behind Dumbledore. So much could be more simple if he talks and gives some explanations....