I think it needs more ways of influencing and maintaining certain moods. Perhaps some injections? Something to induce fear and an aphrodisiac for heightened sensitivity.
Also, more dialogue and responses would be a huge plus. Reactions based on fear and arousal to being cream pied in specific holes, reactions to anal versus vaginal sex. If she's not aroused she could find penetration painful, especially anal. That'd be a huge plus to "painal" fans. Perhaps lasting mood/attitude changes? The ability to "break" the girl through fear, torture, or pleasure and the appropriate dialogue changes for each. Pain/fear should lead to a timid, submissive attitude, afraid of angering the villain. The arousal or 'fucked silly' route should lead to a submissive slave desperate to please the villain and be pleased. There should be appropriate reactions to all interactions based on those factors. Perhaps some 'aftercare' like healing their wounds and bruises, or otherwise soothing them. There could be attitude-appropriate reactions to these as well. Crying with running tears and perhaps make-up would be another welcome addition.
I realize voice acting and such a tremendous library of audio samples is a massive and expensive undertaking, but with a game like this voice or subtitle dialogue at the very least is so important for setting the mood and atmosphere. You want the heroines to feel much more 'human' and less doll-like. That's part of the fantasy, really. Anyone can fuck a sex toy, but the ability to do whatever you want with your favorite, or most hated, heroines is the biggest appeal.
Cumflation and expulsion would be great optional toggles as well. Maybe dialogue that hints towards impregnation/breeding. The whip should maybe have "power levels" similar to the cloth removal gun, depending on whether you just want to whip her more casually or cause real damage. Currently, it's a bit too fatal in my experience.
Finally, and this is my selfish appeal to my own fetish... But I'd really love to have an optional, alternative player model/voice that is a futa, or woman with a strap-on at the bare minimum. Perhaps with different reactions from the heroine, perhaps disgusted or intrigued that their captor is a woman, or shocked to see she's packing that meat-kryptonite.
Sorry for the essay. >_> I only go into this on projects that I think have huge potential. It's an aspect of being more critical of things you really like.