Fan fiction is always a hit-or-miss deal, and I speak from experience. (Just Google my name and you can see real evidence). At worst, it's non-creative, slavish, and not worth the time and effort; at best, it can be creative, provide fresh insights, and allow new talent to develop.
Two great examples are from Sandy Collora, a filmmaker who made a World's Finest trailer and Batman: Dead End. The only bad thing about these films...is that they're trailers. If there was any justice in this world, Mr. Collora would be handed either franchise (although, rumor has it he has received a directoral assignment, although I could be reading Screen Rant incorrectly).
Another one is Star Trek - even in the midst of doubts about the franchise, some of the best work is done by fans. My personal favorite - Star Trek: Renaissance, which takes place in the Federation's "future". Written as teleplays, provided in PDF form, this is Trek at its finest.
Case in point: after a really rough few weeks, I came home to "read" the episode Shadows of a New Dawn. (They even have a primer for newbies). This is probably one of the best pieces of writing (never mind television writing - or Trek Writing) that I have come across in a long time:
the only thing we truly know about the undiscovered countryAll in all, several conclusions come to mind:
is that we know nothing at all. And the worst of those dangers we face, the ones that in the end are the only ones to have the power to destroy us, are those that we face within ourselves, our own personal demons. The hardest fought battles that lie ahead are those for our hearts, and for our souls. It is how we face up to these challenges, and whether we can dig deep within ourselves and find the courage and resolve needed to overcome them, that will ultimately decide our destiny. (By Rob Jelley & James Sampson)