I think this book might be my favorite of all the HP books, even though the ending is pretty sad. I LIVE for backstory and there is SO MUCH of it in this book. I love learning about the Horcruxes(!) and Voldemort's childhood. And this is the book where we see the most of Dumbledore, and he finally treats Harry like an equal, which I love. Plus there's Felix Felicis, Luna Lovegood commentating Quidditch, and Harry being more mature than he's ever been. This book has some of the happiest and saddest scenes of the entire series, and I love it.