There's actually significant backlash against them now that Rowling said some unpopular stuff.

I also don't think people who read them now understand what it was like for the original readers who literally grew up with them. They were unique because they transitioned from books for children to books for teens, and they were a cultural phenomenon, with movies coming out well before the book series was finished.

When my child read the series, she was very young and one of the few in her age group to finish it. Young children often get stuck after book four, while teen readers may find the first books pretty childish.

As an adult, I enjoyed reading the series and watching the movies, but I wasn't the primary audience and I don't read them over and over again. The primary audience was really that one generation of children and teens who grew up with them, and it was perfect for them.

Another criticism I see is that they don't make sense, but I think that's unfair. They appeal to kids precisely because the world they describe is so arbitrary. It confirms their suspicions that adults really don't know what they are doing any more than kids do. It's a satire of the way the adult world works.

Quidditch is a perfect example. It's a sport that makes little sense, just the way school and politics and magic make little sense. It's ironic that quidditch has been turned into a real sport.