My all-time favorite book is probably Deathly Hallows. I don't know why. Probably because, more than anywhere else, it feels like childhood is over. Finally and irrevocably. That there's no way to bring the past back.
I grew up with these books, and I grew up with Harry. And after reading the seventh book, my childhood is definitely over - too adult things and issues are covered in it. Perhaps that's why this closing chord is so satisfying to me.