I dunno, it's always been pretty obvious to me whether or not a fic and writer is pass or fail. There aren't any actual requirements or anything, just quality or writing and enjoyability, really. Note that even original characters aren't bad in nature, but many times quality of writing goes down when badly utilizing an original character. Also, because Touhou is such a malleable universe, it's very easy to not give personality to certain characters, and it's also very easy to overload a character with traits. I know other places criticize the overuse of the Brown Tewi statement, but really that's a big reason why Touhou is so popular and easy to write with. However, because it's almost natural to form views on any character, it's quite easy to have people that don't like works just based on the author's portrayal of a character, like Nobu said.
I find it's much easier to write something totally weird and different than it is to attempt at character interpretations and get away with everyone liking it.
Also, I don't like how you use the expression "True fans".