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?

What I'm still curious about is why Fundies see Harry Potter as bad and Lord of the Rings as good.  Is the the underlying Christian themes in the latter?  If Harry Potter was heavily influenced by Christianity, would it be considered less evil?