Originality and the feel that it's being written with a meaning and an end goal in mind. I ignore every piece summarized as anything like "a trainer goes on an adventure full of friends and fun," but I eagerly jump on anything with a description more like "a trainer who slept in and missed getting his first Pokemon finds unexpected adventures at home that teach him about both humility and courage." I want something with an ending. Endings are beautiful. Don't underestimate them.
Amateur fiction should offer me something that neither cheap used books nor the current hot titles can, and if it doesn't then I have no business with it. I feel a little stuck up saying that, especially considering how much I simply refuse to read or reject after a few minutes of reading, but I grew up in writing communities where people had wild ideas and I read because they swept me away rather than out of a sense of duty (gotta give out those reviews!). It didn't matter that some of the writers were in 5th grade and had the kind of structural problems you might expect. I still have a copy of one from 10 years ago.
I have more respect for people who take wild ideas and fail terribly or offend me than the opposite extreme. Write about a bipolar Leafeon with a chronic farting problem before you write a journey fic centering around John Doe without an end in mind.