To me, an important thing about characters is their presence and demeanour in the world they live in, and how much they fit in. For example, I dislike alicorn OC's mainly due to the fact that they're meant to be quite rare and powerful, which means if they're not designed correctly they just seem to not fit in. For me, a character needs something that makes them stand out, something that gives them benefit and something that flaws them. With the right personality to go with it, this would give characters more depth and appeal to me.
