I feel like I'm one of the few people in the world who doesn't like Harry Potter. I read the first 3 or 4 books (not when they were new) in like a week one summer and they were the most formulaic books I'd read in a long time. How is Harry Potter so big when other formulaic British Children's literature like Redwall isn't?
Because Rowling has reworked some good fantasy concepts, with a
unique interesting twist on good versus evil, and made it a tale of growing up in adolescence (I'm assuming having not read Redwall, that it is different from that). It strikes all the right chords with younger readers and it's actually well written for this type of fare (the same cannot be said for something like Eragorn). If you've read George R. Martin, Tolkien, C.S. Lewis or what have you, these are concepts you've read before, but Harry Potter is not intimidating to your average reader. Trying to get an elementary student to read C.S. Lewis is like pulling teeth, but Harry Potter is a concept they can get behind. It's far less alien and as a kid with magical powers following a generic hero arctype, it's much more exciting.
My brother is diagnosed with some kind of learning disability, and as so, he finds reading a frustrating experience that he usually avoids at all costs. But he sat down and read Harry Potter. I can't hate on that.
The movies are just awful, though. They're pure fan service, so if you're not a devout fan, they kind of blow.