Really nice art! I'm super excited for what UiTC2 is gonna be like, though that doesn't mean I want stuff to be rushed: your wife is right, don't overwork too much, my burnout experiences taught me not to.
Aaanyways, something that I personally like in games are collectibles. They trigger my completionist side and it's always nice to have a reward for getting them all. Plus, secret areas also sound kinda fun. Maybe clicking on a door that doesn't have the "walking symbol" could lead to one? Idk, I saw it done on another adult game called Influencing and I personally found it interesting. Things like that feel really rewarding to me in games because I find it really rewarding to find things out on my own.
And I totally agree with the difficulty thing! Letting players choose whether they want to play on easy or hard-core just makes the experience more...customizable?
Wow, what a long-ass paragraph, anyway, good luck with the game!