Honestly basic levels of maturity and realism. Nothing takes me out of the immersion as quickly as immaturely written sex scenes. I remember playing Fashion Business and the female protagonist was being harassed by her boss. So far so good, but what was the sex scene?... Two girls touching butts. What 5 year old though that was real human sex at all?
There aren't many games that do female protagonist well that I know of. Lust of Passion despite the many, many flaws in their games do get Female MCs. Eleanor, Call Girl, Pledge Naughty Sorority Girls are all excellent in putting you in control of a budding sex worker, party college bimbo, or a slutty cheating wife, because they write the female urges and desires well, and the sex scenarios while fantastical, never devolve into immaturity.
I'm also really liking Lust Campus so far! Not only for the gorgeous visuals, but the story and characters. You get immersed in the fantasy of being a hot college woman, with lots of options for sexual encounters and promiscuity. The game doesn't shame the protagonist, she is just enough in control that it doesn't feel exploitative, and the scenarios are sexy and well written. It's super promising.
That's all I really ask. I like clothing options, customization, etc. but a little realism and maturity goes a long way in making the experience worthwhile.