I think a large part of it is the interesting visuals (well, descriptions of them), like everything being crooked and off base in Diagon Alley, and the silly names, like Diagon Alley. For a kid or teenager, that's pretty interesting and unique.

I actually genuinely think she never expected to write more than one or two books. The first one feels a lot like she was going for something Terry Pratchett-esque, like a parody/comedy version of a fantasy setting. Like, a lot of the silly naming conventions started appearing less and less as the books went on.