I'm pretty sure that the story has to be the most important one. But since we're asked between artwork and animation.
I'd say I'm leaning towards animation more, but of course artwork is important to me too.
Since most H-games seem to not have any animation in them, I feel that art work is more important. Any game that I see that contains animation is usually only feature the same frames being repeated. The only games that I do have full animation that I can remember are schools days and its sequels. I feel that the artwork needs to be more detailed since that is something that animation lacks.
Imagine a videogame like Final Fantasy (type of animation , beautifull 3d, light anime style) with some ecchi scenes. Thats my hope for the years to come. Otherwise, expect the same games for a long time.