Author has written 3 stories for Percy Jackson and the Olympians, My Little Pony, Harry Potter, and League of Legends.
I don't like those "put this in your profile if you've done this!" things. It's pointless, stupid, and not really worth reading in my opinion.
What makes Fanfiction good:
Whenever I "rate" fanfiction, my main factor is how plausible something is. I look for an explanation as to WHY character X is doing this. If it's just random "oh character X suddenly falls in love with character Y", "character X learns how to become godlike on his own", or anything like that, I'll stop reading immediately. I have no problems with godlike characters (it's actually one of my favorite ways to change a story), I just have problems with ones that get that way on their own without any outside help. Because I like crossovers, there's an extra criteria for them. How did X get from world A to world B (if he's dimension traveling) or how does character X find out about characters R, S, and T? It can't be just because the author felt like dropping them off in another world, that's just stupid. I also hate it when the main character knows about the alternate universe the first time they access it. Harry Potter should not know what a Pokemon is unless it is clearly stated that he has somehow played the games. And even then, the timelines have to be played with since Pokemon didn't come out until 1996.
Next factor would be grammar. While it annoys me if there are common spelling and grammar errors, I'll usually keep reading if the story is good enough. I really hate any story that looks like an "its azimnag taht you can raed tihs bcuseae the ltteres are all mxeid up", they should not be posted. I want to read in english, not your crazy foreign language.
Finally I have to like the subject matter. I usually won't read a fanfic where I don't know what canon is for it. Occasionally I'll find a crossover between one that I know and one I don't that I like, but I don't go searching for them. I am okay with romance, but there has to be some action going on or I get bored very fast. Pure romance is boring, I like it better when it's a large part but not the main focus of the story. I like stories where the main character gets super powerful, but as I said above, he needs to have an explanation for how he got them and trained them into usable form. Crossovers are by far my favorite type of story, but there's not enough good ones. I'm also a fan of M rated humor.
All of the above are reasons why I haven't written anything yet, I can't live up to my own standards in writing. I tend to get a great idea for a crossover, then consider the hows and whys and it falls apart. I also tend to read much more than I write, so anything I do write will take a while to update.