'Splain, please.
hentai? yaoi? yuri? eichi?
No really, I consider fanfic to be mere forms of entertainment, the kind of thing one indulges in like those bodice-ripper books I used to sneak away from my mother's bookshelf because I was so utterly bored with what I had already. Nothing deep, nothing demanding, just fun stuff. Out of anyone who likes fanfic, I am probably pretty severe in my dismissal of it EXCEPT when its a piece that plots itself solidly within the original story...the best way i can explain this is to use an archaeological term : in situ. If the story is written so that I could very well believe that it is in situ of the original work, then I pay it closer attention.
This one beats em all that i have read, imho.
You must not hang out around fanfiction sites run by 15 year old girls. They have adopted a series of Japanese words to explain story content. (This holds for every genre I've ever been acquanted with. Even Star Trek. The terms spread quickly.)
Hentai is a generic word meaning "perverted". Nasty stuff you don't want kids to read. Yaoi is homosexual romance. Yuri is lesbian romance. Eichi means mildly squicky - ie, just a little perverted.
I don't like bodice rippers... but some fanfiction is better than that. I consider fanfiction worthwhile if the author has taken care to preserve the characters as they are in the original. For instance, my favorite piece of fanfiction, back in the day, was a "Harry Potter" story that really only focused on one minor character and used the world. It worked really, really well. (Even if it was slightly eichi)
But LotR fanfic crosses some inner line, for me. It's kind of like Bible fanfic, or "Iliad" fanfic. Or Shakespeare fanfic.