The genitalia of the models are great already, but I highly recommend some improvements:
1. make the labia really move around the cock's shape. That means the labia close up when there's no penetration, but spread apart when sitting down on a cock, so it nicely grabs hold of it.
Right now the labia are in a fixed position, so it doesn't look realistic.
2. Add foreskin to the males, the foreskin should move backwards when the penis gets stiff.
3. The guy's penis should be able to change naturally and realistically from flacid to stiff and vice versa.
4. Add vaginal/penis fluids. For example when the excitement meter is high there should be more moisturization coming out of the vagina, precum from the penis and coat the penis with a wet substance.
5. Breasts should jiggle depending on the size.
6. Add the posibility for players to directly touch and stimulate models by using the mouse curser which should immediately and automatically turn into a hand icon.
When u move the mouse cursor over a woman's breasts, ass, belly, or head then you should be able to massage that and she should react to it with some soft moan or get shy/ giggle etc. Stroking her head should make her smile, become happy.
7. Also the men u should be able to stroke their cock from flacid to erect with the mouse cursor.
8. you should be able to immediately finger of rub a woman's pussy with your mouse cursor.
9. Realistic facial expressions that are convincing and fit the model's personalities.
10. More variety in the moaning sounds so you don't hear hte same thing over and over.
These improvements will make Sex Sim much better, and more enjoyable!