For me, it's characters - above all else, you have to make me care about your characters, and that goes for every single genre of anime. They can be wonderful people, they can be terrible people, they can be laser-focused on a single objective or just living their day-to-day lives, but an anime absolutely must get me to want to watch those characters do their thing, whatever that "thing" is. You can have all the grand conflicts you want going on, all the wild powers you can imagine or the most incredible animation ever put to screen, but if I don't care about the characters caught up in those conflicts or wielding those powers or who are so lovingly animated, I'm not going to stick around.