Just played the game, and all I can say was that was a great experience. Still, a few things have stuck out to me, and I just figured I'd give my two cents on what could be improved.
1. The grind. Holy moly the grind. I would suggest changing the amount of money the player earns from teaching a class from $25 to $50 or $75, which in my opinion would make things far more tolerable. Without cheats or the strip club, it takes forever to earn a decent amount of money for serums, etc.
2. The sex shop. One of the things that was confusing to me is how underutilized the sex shop is. We use a variety of sex toys on the girls, yet we seem to get them automatically, with no effort. Beyond the two clothing events and Francesca, what purpose is there to the shop? I think that with increased earnings, it would make sense to make you buy the toys for your 'tutoring'.
3. Thirdly, the stage 3 states for Yuki and Harley feel lacking, especially when compared to Kara. Also, compared to their previous states, there's not as much you can do with them. I don't know if you have more content planned for them, but I know I'd appreciate it.
4. I feel like there's an over-reliance on the body transformation formula. It's the formula used the most, and I'd love to see the Mood and Lust formula get used a little more.
5. Finally, a 'storyline' issue: I feel that some of the corruptions don't always resolve the issue or reason that the player takes advantage of to get close to the women. Take Kara and Yuki, and compare their end-states to Chrystal's and Harley's. Yuki starts out kind of depressed and aimless, and you taking control of her life gives her a purpose. Kara has her career and personal life damaged by you using the serum on her, and her embracing your ideas helps her get her home and job back. Problem identified, problem solved. For Chrystal, I don't get the sense that the 'tutoring' really helped her grades, or anything similar. And Harley's 'wannabe BDSM writer' element doesn't play any role in her final corruption phase. I loved Harley's corruption path, and Chrystal was a good starter character, so I hope that you guys keep that in mind for characters already in the game and in the future.
Suggestions:
Keep Luna as a switch, rather than a total domme or sub. She really adds some variety, and I hope her tattoo parlor will be used in the future.
Maybe add a pair of girls to train (as in, you'd train them together). I know there are plans for some F/F action, and Luna kind of fills that, but there would be a different dynamic with, say, two clashing roommates or students with some serious disagreements, which would be fun.
Another teacher or faculty member would be cool. Maybe someone on the school board, or a rival professor?
That's enough for now. This is a great game, and I really look forward to seeing what the next update will have.