The trope that annoys me the most are the same family, different universes in every incest game.
Mom: Bombshell. The definition of milf. Big tits, big ass, and the personality she has is making you clean you room and being sexually repressed. "Oh Timmy, I was just walking by and you left your door open even though you're naked. I know I shouldn't look, but your BIG FAT SON DICK makes me so wet!" Then she masturbates after seeing her son's penis while the son ALSO walks by with the door left open. Its all very lazy, samey, and I'd love to see a flat-chested mom for once. Or even SHORT. Why are all mom's 6ft tall?
Older Sister: She's bitchy. She smokes. She parties. She's got a boyfriend. "Fuck off, dweeb." And guess what, she's just aching for someone to take control of her. Of course she wants that to be her BROTHER. Who else can satisfy daddy issues incarnate other than the boy she's related to and three or more years her younger. As long as you got a big cock and blackmail her about whatever it doesn't matter, she will choke down all the brother dick she can get.
Younger Sister: Innocent. Borderline retarded. Cutesy. "Brother, whats a penis?" And guess what, for the low low price of telling her its just for practice, she will offer up her vagina to the first person who wants to play doctor. They almost have no personality other than either being easily corruptible and stupid.
This type of family dynamic is so common in incest games that it just generally turns me off to the games that use it now.