For me the most important thing is imagery. As long as the girl is hot and the art looks good, I don't really care about the script. Well, I guess VA quality also makes a big difference, moreso than what's actually being said. I also don't care if a scene is relevant to the story or not, if it isn't I can just go back to it later in the replay mode.
Another really important thing for me is that both (or all) parties are having a great time. Rape doesn't do anything for me. Best is when Protag-san just completely fucks the sense out of a heroine, in a good way.
As a last thing, I'm not quite as pessimistic as many people here when it comes to "all scenes are written in the same cliché way", I actually think there's quite a bit of variety in it.
Of course, none of this matters as long as there's ANAL