I'm a millennial who grew up alongside Harry. These books are what made me fall in love with literature, were my escape from an unhappy adolescence, and they mean more to me than any other pieces of literature. The last time I read this novel, I was curled up in bed in my room, feeling a lot like Harry himself - alienated and vulnerable, grouchy and socially incompetent. It's impossible for me to be objective, here. I'm not sure what I would rate these novels if so much of myself wasn't wrapped up in them. I kind of feel like I'm looking at myself through the other end of The Mirror of Erised (okay, my life isn't that idealistic, but adulthood looks pretty damn good in comparison).
No, these books aren't perfect. Harry is a tempermental toad, for one (especially in The Order of the Phoenix, good lord, the teenage angst). But the characters apparate in front of me whenever I open the pages. When Rowling descibes Hogwarts, it feels like I'm entering the same headspace as my teenage self, where I made another home for myself. It was lovely to be back.