If you had to separate artwork, animation and story, I feel like the most attractive part would be the artwork. It immediately catches your eye, and it reels you in to be interested in what lies ahead. What's the story? How's the animation? Artwork also holds in itself bodily fetishes, like if you were into flat chests but not huge titties, and you came across an oppai game, you'd instantly close the tab. If the characters looked like they were drawn by children, then the whole thing would be in shambles. Shitty stories can be partially saved by amazing artwork, and games have lasted without animated CGI for years.