Wouldn't call myself an expert, but if you're looking for advice, following would be what I've give to improve your sex scenes;
1) Games with good to great sex scenes have decent amount of buildup & foreplay.
So french kissing, kissing on neck/body, handjob, blowjob, footjob (not my kink but for some folks it is), 69 position, etc etc, provide a great setup towards the main sex scene.
Hence, avoid transitioning too quickly into the main sex scene.
Doing so, just shortens the whole ordeal.
2) Experiment with different sex positions
Obviously, missionary and doggy style goes without saying, and there's also different positions such as spooning and others.
For this part, you'll need to do some research to find different sex positions and mix them up with the sex scenes
For example, one of the other games I'm following, Pale Carnations (which might actually be a good game for you to learn from, great game in terms of story, and it has tons of sex scenes which is quite creative I'll say), uses a Strong man sex position.
Don't think I've even known such position before I played that game.
Given there is magic involved, who knows.
Perhaps in the future, MC and a LI may have levitation sex while floating in the air?
3) Lengthier the scene, the better.
Unless the story forces the sex scene to be a quickie (e.g. MC fucking one of the LIs but that LI doesn't want others to know they're fucking hence they're doing it in secret), it is more beneficial to have the sex scene to be longer.
Just gives more satisfaction to the player watching.
4) Have the occasional close-ups with different camera angles of the pounding during sex.
This can be seen used by devs in some other games. MC's dick pounding the LI's pussy like a piston during sex, whether the camera angle shows it from the front, or from the bottom with a "worm's eye view" (for positions like doggy style) with the close up shots of the penetration greatly improves the hotness of the sex scene compared to just the wide shots.
5) Show the creampie or cumming outside.
This point relates to the previous point.
When the MC cums (whether inside the LI or outside), close ups generally greatly improves the sex scene.
If the MC cums inside the LI, have the close up of the vagina with the cums dripping out from LI's pussy.
If MC came outside, show the shot (though I guess not closeup as much as pussy shot as when came inside) of MC making a mess on LI's stomach or back (dependent on the finishing sex position I guess missionary or doggy style etc etc).
6) Avoid using cut to black approach
With this I'm referring to the second Aria sex scene in the abandoned fortress.
Sure, it's obviously implied MC & Aria had sex for the second time, but honestly? I think it would have been far better had you just either done the full sex scene (even if the release of the update took longer due to it), or not have the sex scene at all (for e.g. not sure whether it would align with Aria's characterization, but perhaps she just wanted to.....cuddle before falling asleep or something).
I don't mean any offense by this, but the whole cut to black approach just gives the impression you're doing shortcuts for sex scenes even though it may not be your intention.
I don't think that's something I'd recommend; sure, many here are along the ride for the story, but I'd imagine people want good sex scenes also, and this cut to black approach just doesn't help at all.
In fact, if you're looking to change/improve any earlier parts of your game now or in the future, that MC-Aria fortress scene is one of the parts I'd say is better off changed (to either full proper sex scene or no sex scene).
This somehow became a bit of long-winded post.
But I hope this constructive critique/advice is helpful at least to some degree.
p.s. Pale Carnations by Mutt & Jeff is the game I used as example here; there should be other games as well which have great sex scenes, but atm, it's the game I think comes to mind most in terms of how to improve the sex scenes aspect of your game.
