There is something about the phrase "Harry Potter Fan Fiction" that strikes terror into the heart. I didn't like the actual books much, even after making allowances for the fact that they're for children.
And yet... It is a work of genius.
The first book I have ever managed to read cover to cover on a computer screen.
I don't know how much of the real thing you'd need to have read to understand it. Not much, certainly. Probably the first half of the first book would do.