If I had to pick one I say graphics takes the easy win on this. I love a good story, but If I'm trying to get my rocks off I need good visuals, not good writing.
70% Graphics and 30% plot, because I see the attractive design to play and after playing I see the story but here the effort of creating its text almost doesn't matter anymore
Graphics brings people in and can even keep people interested if it looks good but really they need both otherwise the game is boring. if anything people play adult games for the plot, because other forms of erotic content usually have better graphics.
it 100% is a balancing act to me, some games could have amazing stories but if it is painful to even look at or ugly as sin designs im out, inversely, it could have the best graphics, hot as hell models etc, but if the story/writing is garbage, ill drop it
For actual games story is the most important to me. for porn games, definately graphics though interesting ways of inplementing the fetishes I enjoy are what keep me coming back.
This is kind of like the personality vs. looks debate. Both are equally relevant. I wouldn't play a sex game with terrible graphics regardless of how good the plot is, or I may play it for way different reasons than the usual. I do enjoy a good plot, I won't enjoy a game just because it looks good. But I won't sexually enjoy a game either if all it has to offer is plot.