There's some bad ones, there's some good ones, there's some disturbing ones, there's some that stays close to the fandom. Its a mix bag. I read a few ファン fiction and I written a few (bad ones though xD).
Depends on the 書く style, point of view, and what it is about. For me i like crack ship fanfics または fanfics of my otp's. I lean もっと見る towards the mature fanfictions as well.
I 愛 to write them and 愛 to read them as long as they aren't graphic, disturbing または go into too much detail on some topics. On a whole I don't mind them
The same as any type of writing, for the most part. There is high quality work and low quality work. Some people do it for fun, while others take it very seriously. Fanfiction has been happening for decades--centuries, really, depending on how あなた define it.
I 愛 ファン fiction especially when it makes あなた feel the emotions the characters are feeling または if it is just super good. In fact, I'm 読書 a ファン fic right now. GAILEE FOR EVER!