Not necessarily games, porn stories as well. The scenarios below are not mutually exclusive, some games/stories combines several aspects I mention.
1. Mother/son: The great pretender. Scenarios when the son makes advances and gets progressively bolder while the mother pretends to ignore what's going on but silently allowing the son to continue. That's basically the template of
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and I love most of them. Bonus points for "let me rub something liquid and oily on you" scenes. I'll never get tired of these.
2. Mother/son: Man of the House. The (mostly female) family is falling apart, but guess who will save the day? Exactly. I'll not argue about the execution, but the incest premise of Zombie's Retreat is perfect IMHO.
3. Mother/son: Dominant son. I love my MCs bold and secure and dominant, and a son dominating his mother is amazing if pulled off correctly. The mother doesn't have to be a complete pushover (in fact, dominant moms are hot if they submit eventually), but in the end I want the son to come on (the literal) top.
3a. A variation of the bullet above, but the mother
is a complete pushover. She can be either naturally very insecure, very eager to please, or maybe a little soft in the head. But sometimes the pushover mom is hot.
4. Father/Daughter: Practical strangers. I find is strange myself, but "normal" father/daughter incest does nothing to me. The rare scenarios I can enjoy are ones where they were not in contact for long years, perhaps one doesn't even know he/she is related to the other.
5. Bonus points: impregnation.