Ambrus said:
I'm still utterly mistified by Potter's mass appeal.
How about this: the books are easy reads, and really quite enjoyable. She writes directly to the experience of her target audience, in that she writes about going to school, having good friends and hated enemies, teachers you hate and teachers you like,
and she plays into the wish-fulfilment fantasies of the same kids (who would
really like to be able to do magic, encounter unicorns and griffins, and so forth).
As for the continuing appeal of the books, she's managed the neat trick of gradually upping the maturity and complexity of her books as the series has gone on, so that they age with the target audience (this may make for some problems for parents in years to come, when their kids are ready for books 1&2, but quite some way from 4-7).
Additionally, she has two things going for her: the Harry Potter story seems to be a retelling of the same Hero's Journey that is found in Star Wars, Lord of the Rings, and elsewhere. It's a story that has repeatedly proven to be extremely powerful.
Secondly, as regards the mass appeal of the books: once something reaches a certain level of popularity, it feeds into itself. If every kid in school has read, and is talking about, Harry Potter, you don't want to be the one kid who hasn't read them.
It didn't hurt that the books were attacked for the 'Satanic elements', of course.
Edit: Pressed 'submit' far too soon.