Give me a romantic harem with a corruption/seduction element that actually handles the poly aspects of the harem well and i'm sold to be honest.
Incest isn't a must anymore, if the game is good in it's own right then i'll try it anyway.
BDSM, dominance and corruption can easily go too far in a game, personally a little of all three is better than a lot of one IMO.
I'm going to break with the convention of either hating or loving NTR and say it's just boring, it's often written very badly and hasn't spent the time to get the player emotionally involved in the girl getting stolen, NTR bad ends for games works for me, whole games focussed on NTR don't, similar story with cheating oriented games.
Trans is tough to judge, if by trans you're thinking Futa, then we all know you've got a solid audience.
Finally as for voyeurism, i'm not sold that you'd be able to make a game sufficiently interesting that heavily rellies on this fetish, it's a nice element in a broader game, especially in a corruption game in which you can use voyeurism and exhibitionism to disinhibit a character but outside of it's use to further another goal i don't think voyeurism and exhibitionism can stand on their own like other fetishes can, great "support fetishes" though.
