What I do know is that several sessions with one will start to make it easier to get her riled up. Foot stuff doesn't get me off but it's the fastest way to get the girl horny because all of her 'orgy system' slots are open, you can apply a tongue or a toy to every slot.
Then her level of arousal (the yellow bars) is applied against the thinner blue bar (her stamina I guess, like yours?), and if you max out her arousal every time you cum in her pussy or ass, then you'll get her to orgasm, though the animations don't really seem much different, you just get a different final "evaluation" type anim.
Honestly I think the anims are great, the dirty talk is cool, wish each of the three at least had different body types or at least different tits.
Once you've just gone hog wild on em a few times though I keep wishing more anims or positions would unlock but I don't think that's the case. I really like some of the start screens you get after a session, like the lewd makeout one.
I know that sounds lame but a little bit more progression would be cool. Unlike the HS model where you just do whatever and the girl is basically just a toy (don't get me wrong, it's sexy), this game seeming to have an evaluation of you actually trying to impress a succubus seems like the unique angle and sort of a missed opportunity to expand.