Why was Harry Potter so successful?

It's a simple question,
Why was the Harry Potter series so successful?

I mean, it didn't add anything new to the genre, and there are a lot of other better series, with better character development and what-not.

I'm not saying its bad, but what makes an almost average book so popular?

>>5
Yeah, but there are a lot of entertaining books out there that nobody has heard of.

Marketing muscle helps, I guess. Someone high up in the publisher of Harry Potter decided to push it.