Well, my welcoming you on board may have been premature (for now, although that is implicit in the very word), but I most decidedly welcome a discussion on what makes an erotic game a good erotic game.
After reading your clarification, I can say our postures are not as opposed as I first thought. If sex must be a key element on a game, it certainly needs to come across as such during a playthrough. The easiest way to do this is to get the main characters on a sexually charged atmosphere, but that can mean a lot of things. For example, one of the most erotic scenes I have played was in "Tsukihime", a visual novel centered around the theme of vampirism; the main character is investigating a series of murders that are taking place in his hometown at the behest of a vampire girl whom he killed at the beginning of the game (the plot is... complicated), in the scene, they have agreed to meet and, when the girl appears, she is suddenly tempted by his blood. The main character knows he can die at any second, and knows that he is completely powerless to resist the vampire if she chooses to bite him, but the life-or-death tension in the monologue is intertwined with an extremely sensual description of the way her body feels pressed against his, the scalding breath on his skin, almost making him wish she would take the last step just to feel her lips pressed against his neck... And now I will need to bash "Twilight" for a couple of hours just to feel manly again. Great. Just what I needed.
Of course, that's just an example, and not a particularly good one because there is an all-ages version of "Tsukihime" without any of the sex. So, even though I can agree with your message and your stance on the subject, I can also think of a few examples were the games were great as both games and erotic games, maybe part of the problem is that that isn't always the case. For example, talking about "Medusa's Curse" RPG combat, what you describe is the typical grinding frustation that has left me unable to conclude Final Fantasy 6. That game is one of the most recognised of the franchise, but it just felt like a chore (something that many erotic games end up being) although that is more a matter of poor game design or limited resources than the concept per se being inferior to a sex centered mechanic/setting.
Completely sexual/erotic games have their place and certainly help maintain the suspension of disbelief required to enjoy them. For an RPG, that may mean battling an army of succubae or something akin to it (Corruption of Champions, anyone?) and for a shooter... I don't want to think about it. Bad memories. But storylines that involve you, that make you feel a wide array of emotions, can enhance the sex by sheer contrast or by nuancing it. It's not the same thing to have a one-night stand with a woman you met in a bar that to desperately cling to your shield maiden the night before a battle with an uncertain outcome. Both can be done brilliantly and in a myriad of manners, but, ultimately, I think it's more a matter of choosing what feels right for the characters than anything else. After all, if we didn't care about their stories, there are plenty of pretty pictures to look at online (and, if we only cared about the stories, there is an almost equal amount of written erotica to be found, so I guess it's not that clear cut, either).
To summarize: I agree with the sentiment of your post, I am eager to try your game and I am a long-winded pompo- I mean, the discussion has many angles to consider. It's not a black and white thing, and, as usual, depends on what you are looking for in the game in question. Now, to find someone who openly enjoys "Twilight"...
Agrippa