Anything that can make me feel interested too that specific anime.
If you've seen my watching list, you'll notice that I watch more than 15 titles each season, and not all of them are story-driven. I honestly don't like limiting myself to just one or two "qualities". I love watching animes, and animes comes in different "shapes" and "sizes".
For example:
Most people "avoid" Kyoukai Senjou no Horizon because of the confusing world, on the contrary I love Horizon for the same reason. By tackling the confusion head on, I learned that it's an awesome anime (and most people in Japan, looking at the Pre-Order rankings.. lol)