The fact that Harry Potter is one of the most popular series in the world of fanfiction says a few things about what fans feel about it. For one, it is always a good sign that people enjoy a series so much they want to read and write more about it, and it is a testimony to how good the original piece is. Another point one can make is that if a series has a lot of fanfiction based on it, then fans find there is a lot they would change or expand on, so they attempt to do that in their own writing.
When it comes to the Harry Potter world, while there might be many things fans would want to change, there is also simply a lot to explore beyond the words written on the actual pages of the books. Take this interesting premise from a Reddit discussion for example, in which Potterheads shared what they think would happen if Dudley had a magical child of his own.
Keep scrolling to read the full discussion. After you are done, click here for a geeky collection of fantastic Doctor Who memes.