Can only speak for myself, but the attraction to incest is completely unique to gaming and live-action porn - I'm not hiding a secret lust for my own mom and seeking a vicarious outlet for that, but for sure the taboo aspect is the turn on for me. So the characters having a recognition of the 'wrongness' of their actions is vital. If you just horn dog it, there's no real distinction between an incest game and a game where you just boink ladies. ('roommates', etc) Proceeding despite the ethical and moral taboo is the attraction. Just making it an exercise of 'sex-as-a-verb' is dull. Some games do it better than others (I think that's one of the main reasons why I like SS so much), and some games start off doing it well and then trail off (Dating My Daughter has gotten a bit trite imo).