I'm of the opinion that the world of fan fiction is a cesspool of preteen fantasies gleefully mangling the original stories and characters that they claim to be fans of. It is a challenge to find a story worth reading where the characters are recognizable and intact as well as the stories and world that supported them through their initial life. I admit that I am a stickler for canon content, for if the characters are not themselves, who are you a fan of and are you writing fan fiction at all?
However, I think fan fiction is a wonderful outlet to explore the question of "what if", to show our love for a creation through creativity, and pay a homage to both characters and creators. I strive to add some fresh content to the pool through my writing - I am an easily distracted college student, but I hope that soon I shall begin posting stories.