First off, I really like what I see here. The character is cute, the animations are hot. This game could turn into something really great.
Gameplay Feedback:
1. Checkpoints/movement. Clearly the game isn't some fast-paced Metroidvania or something like that, with the movement and combat having a more deliberate pace. That being said, as the game moves along it'd be good to implement points that you can travel between in order to get to a environmental sex scene or enemy in that location. Since movement is slow, it takes a long time to get from place to place. Going all the way from the start of the game down to the basement to see the flies (or the girl in the corner with the fly) takes inordinately long, and that kind of situation could be fixed by adding a fast travel system so you can go back to places you've already been to.
2. Extra space and exploration. There are certain places in the game that are out of the way, but offer no reward to the player for going to see if anything's there. Take for example, the left side of the corridor once you go down the rope. There are two female zombies in the way, but after you take them out, it ends up being pointless since there's nothing there. If going in a direction is pointless, then personally I think it'd be better to just block off that way entirely rather than waste the player's time, especially since combat and movement are slow. No space in a game like this should exist just to exist, they should serve some kind of discrete purpose.
3. Combat. I don't expect the character to do any crazy martial arts or anything, but an alternate weapon swing animation would be nice. Maybe add some forward movement when you attack because the enemies reel back quite a bit when they get hit, especially the female zombie. When you run out of bullets, consider adding a small prompt near the weapon icon that says something like "Press (key) to Reload!".
4. In the basement your shirt ends up being the same color as the wall, so it looks like the player character's torso below the arms is invisible.
Realistic Suggestions:
1. With the sex scenes, I already like them quite a bit. I do like that you can have the character lie there in their after sex state as long as you want rather than being forced to automatically get up. However, there should be a button for the enemy to start having sex with the player again, and also you should only have to press X once after sex to get up instead of still having to mash it.
2. The combat in a lot of these kinds of games tend to devolve into walking up to an enemy and then hitting the attack button X number of times, which can quickly get stale. Since you've already implemented the ability to attack at different angles, perhaps make attacking different locations produce different results: hitting a zombie with a low attack might temporarily knock it down to help you with crowd control. Something so that combat doesn't just become "walk up to a zombie, 1-2-3-4-5 hits, walk to next zombie, 1-2-3-4-5 hits, etc." There's no real way to avoid combat like there is in, say, the Resident Evil games, so the combat itself has to be a little more interesting.
3. It's not optional, there absolutely must be a way to make text immediately appear in the dialogue box rather than being spelled out one character at a time. And there must be a way to skip dialogue. I don't think I have to explain to anyone the annoyance of hitting a button and the dialogue NOT coming out any faster.
4. How about some more oral scenes? Could even have its own section in the status screen, how many mL of semen swallowed.
Fantasy Requests:
1. Corruption system? As the player character has more sex, they grow to enjoy it more with some variations in dialogue or possibly in animations too (maybe only 2nd/3rd stage to reduce workload). There's already a bar in the game that can serve as a a corruption meter (the sex progress meter when not engaged in sex).
2. Voluntary sex? This could also tie in with a corruption system, or just exist as its own thing entirely (maybe get used as a way to avoid taking damage). It'd be really nice if the character could offer herself up, perhaps even be the one initiating sex with the enemy (blowjobs!). Maybe it wouldn't even have an alternate animation for every enemy, but even without that it could be a means to get past an enemy (or a group of enemies) without taking damage. It could tie in with the corruption system to balance it like if you have too much sex and get too corrupted, your character ends up having a game over because they can no longer continue because they're just too busy using those orifices. Then corruption itself could go down with each enemy you kill, and since enemies respawn you could basically control how corrupted you want to be.
3. Semen stains during gameplay? The player character gets visibly more covered in fluids as they have more sex. Able to use a bathroom sink to clean themselves off if they want.
4. Alternate costume/nudity. Of course, this one's a real fantasy because of how much extra work it would be.
Other thoughts/Bugs:
1. Please, NO GORE. I hope this game doesn't end up having any guro elements in it. There are so many games that are completely ruined for me because sex is suddenly combined with gore. Reminds me of the scenes in Urotsukidouji where a girl's being raped by a monster, and then they end up being torn in half or something. Might as well have torn my boner in half too. Judging by what's in here so far, I get the feeling that you might have the same view on that subject as I do.
2. When attacking multiple enemies, if you attack too quickly you end up not hitting anything at all even when an enemy is clearly in range.