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?

They indeed did put across a new idea. The beautiful notion that a ragtag group of Death Eaters can successfully capture a Pumkin Patch Daycare center and perform butt gapes on every wizarding couple's infant child. Lucious Malfoy himself hexed his gnarled chode with the forbidden curse, trastifficus toephallus, which gave his meat extra girth as well as smelling like sweaty foot soaked in vinegar and Cheetos.

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