I have all the opinions.
Alright! So, I grew up reading these books. Heck, I was probably only seven or eight when I finished the series. They're nostalgic, which means that I'm biased towards them, but that doesn't mean that the only reason I still love them is because of the nostalgia. Quite the opposite, actually. I can still read back through the books and find something new--obviously, nothing as new as Brandon Sanderson's books, but new nonethless. I have a bit of an advantage on my arguments here, as I'm an aspiring author, and just the sheer amount of foreshadowing in each book is amazing.
However, I'm not what you'd call a Harry Potter fan.
Fadran, you lied to me???? I hear you demand. You have a Ravenclaw banner over your profile picture, and you're NOT A HARRY POTTER FAN???
No, I am not. I am not a Harry Potter fan.
I am a Wizarding World fan.
The most charm in J.K. Rowling's books comes from her world; the Wizarding World. The random jobs in the Ministry of Magic, the secret passageways in Hogwarts, Howlers, Remembrals; WANDLORE, STORM IT. It's so much more than a story at this point; it's a world that you can immerse yourself in with your friends and family without people looking at you like you're a crazy person. You can go back and relive your childhood of waving around a stick and yelling expelliarmus without somebody telling you to 'go grow up, already.'