This is an interesting long thread. I've just found it and read it all. Impressive.
As one of the oldest people here, it seems funny, differentiating between adult and juvenile fiction. As I get older, I find there is only good and bad fiction, good and bad art. Good art and fiction is good because it tells the truth. Bad fiction and art lies.
Harry Potter is one of the most enjoyable series of books I've ever read, and I've read all seven books, out loud, to a young relative (My Hagrid is better than Robbie Coltrane's, and my Dumbledore is better than Michael Gambon's--but not Richard Harris's, rest his soul). There is a remarkable adult theme to the books--that you never let the rules keep your from doing the right thing. It has depths to plumb if you know how to plumb them.
It's hard to translate between media. Things have to change. Filmmakers make decisions. I never agree with all their changes. I find that I love the Potter books and that I like the Potter movies. But I own them all, and experience them over and over again. Delightful.