This game was pretty fun, rng gave it some replay value and some of the challenges were pretty interesting (also kinda progressive difficult in the sense that easy-mode is just learning to beat each mission no matter how long it takes, and then you can progress to trying to beat the challenges and beating quests in a single day so you can get the most out of a single playthrough).
I haven't finished the game yet so maybe those things are already in the game and I just haven't found them yet, but there are two things I would like to see:
1. Easier way of triggering the scenes. Personally I would make it a "challenge star" or "newgame+" unlock to have it be some kind of portable radio, so you can send characters to a location without needing to be in the same tile as them nor sending them on a mission. It would make some puzzles easier (or at least more consistent since there won't be the risk of the character you needed for something taking a stroll on the other side of a large map and costing you several turns), which is why I would make it a late-game unlock.
2. An upgrade that lets you hear the "muffled" dialogue when peeping on a scene. I get the appeal of partial dialogue for the voyeur fetish, but I also wish that eventually there was a way of listening to the full conversation between the characters.
Also this is more of a personal preference and I understand if the dev doesn't want to do it so they can stick to the genre, but I would like it if there were non-voyeur scenes, I don't like it when the MC is completely detached from the scenes in a porn game. I can be indifferent to it when the player's character isn't very involved with the other characters or doesn't have much of a personality, but I like the characters in this game and how they relate to the MC so I would like to see them interact more (inject more of the futanari sister teasing the MC directly into my veins).