Thanks for your feedback. Most of my experience comes from developing mobile games, and this is my first project for PC. My knowledge of NSFW games is still quite limited. I’m planning to release a major update to improve both the content and gameplay. And I think I’ll need to play more NSFW games myself too.
With that in mind, here are a few things that are often sore points for players of these kinds of games. For the most part, it's the UX stuff, but there are some content-specific things as well. Apologies up front - while my points are valid, I can get a little wordy at times. Sorry about that.
*Content* No Gallery of any kind - One of the most common issues. Players enjoy good gameplay, but let's be real - we're here for the H-content, and no matter how great it looks, plays, or how good the story, you might get 3 out of 5 if it doesn't have a gallery for the H-scenes - we're trying to make a sticky mess, ya dig? There are lots of games that are very mid, but they get 4 or 4.5 out of 5 just because they have decent H-content and a gallery to replay it. Galleries for your H-content are worth their weight in gold. And if, for some reason, making a gallery causes you any problems, the next best thing would be something like hard-coded save points right before such scenes that only activate in the load menu once a player sees them once. Not a great alternative, but it would be something rather than nothing.
--- Tangent: If you have H-content that isn't limited to specific scenes, such as traps or combat sexy time, you might consider a simulation room or something of the kind for the non-scene content. If some of your hottest material isn't in a scene, and your gallery only covers the contents of the scenes, it's a missed opportunity in my opinion.
*UX* Control scheme - I recommend providing a way to remap controls (proof of concept - someone already complained about controls). This is a UX thing. If it's easy to use or easy to reconfigure to make it easy to use, players are more likely to speak positively about the experience. The ability to reconfigure controls is a creature comfort, and most of the best games provide this feature.
*Content* Lack of diversity in fetishes - The biggest limiter to your audience size is what you're willing to put in the game. I'm not saying you should include anything you hate, but if it's things that you're indifferent to, at least consider putting them in. Ultimately, it's your game, but the more you put in, the more people you'll touch... or, umm... inspire to touch themselves...
For example, Scat is one of very few hard-limits I have, though I know it's a fetish in certain circles. It wouldn't be in a game I'd create. I'm indifferent to NTR and not really favorable toward Futa, but I'd be willing to put some of each into a game if it gave me access to a wider audience. If you build it, they will cum - hopefully several times.
*UX* View control - A couple have already commented about camera motion sensitivity or screen boundary issues, but my comment here is more broad than just sensitivity. Bad view angles, awkward camera motions at the wrong times, parts of the play area that limit camera motion or force a specific perspective and thus restrict a player's ability to see enough of the map to progress through an area or do a certain thing - players will take away a whole star just for bad camera control. If I wanna see her titties bouncing, but the camera is showing me a dude's asshole, you may as well be shitting on my face.
*UX* Sound effects and controls - It's really a shame when developers combine different types of sounds into a specific sound control, where a player might want to turn one sound type off and keep another. Like moaning tied to BGM, or general voice tied to general game sound effects. Maybe I don't want explosions, gunshots, clashing of swords, etc., to be all too loud, or perhaps I don't care about BGM, but I do want to clearly hear what a character says, or when he/she moans during a scene.
There's more than just this, but these 5 are probably the most frequent issues I've seen others complain about (and I've personally probably complained about at one point or another). And again, sorry for the word-bombing - I hope it wasn't too much.