Without a walkthrough, this is a 1/5 for the absurdly large amount of backtracking, with a walkthrough, this is a 5/5. So my rating is the average of those two, 3/5.
Here's a link:
https://f95zone.to/threads/parasitic-evil-v2-18-rs.184376/post-12397016
Story:
So, the story is, in a genetic experiment gone wrong, you meet a young woman who is infected, the only temporary cure is the main character's sperm. You navigate around the hospital, avoid or shoot zombies, search for key items, unlock doors and floors and so on, and look for a way to escape the hospital. You get a happy ending when you escape.
Gameplay:
You search for items, hide in safe rooms, hide in lockers, find notes, fight or run away from zombies, farm points to acquire upgrades, collect money, bullets, healing syringes. You have to disinfect your girl companion with sperm from time to time to avoid hitting a game over. In terms of gameplay, she is completely useless and serves no purpose, but this is a porn game so you cooperate with her. There's infinite money spawning in rooms, there's vending machines to buy everything you need. In combat, you gotta either kill the enemy with 3 bullets, or heal up, or reaload, or run away and hide somewhere. You will find zombie traps on the ground and zombie eyes trying to see you and send zombies after you. There's a noise mechanic, meaning if you run of shoot you attract enemies, if you walk calmly or stay still or hide you don't cause noise, but this is kinda weird because you can remain still without making noise and yet the zombies can still find you, this is not explained in the game at all. Some enemies are immortal and you can only stun them for a duration, the big boss cannot be stunned at all so you gotta bail. There's a boss fight at the end where your skills really are put to the test, in combat you can also dodge to avoid incoming attacks. As you progress you will collect upgrade points, you need pretty much everything so that's interesting.
Level design:
it's stupidly hard, and realistic. You explore hospital floors one by one, but you have no map so you are completely blind, you need to quickly find a map and then start searching every room to get all the things you need. Sometimes you will see that one door which just wont open no matter what you do, that's because it requires items from the next levels, with backtracking. The last puzzle in the game with the colour separating is glitched if you fail it on the first try, you gotta reload, which is very very dumb. It took me 4 sittings to finish the game, cause on my 4-th sitting I picked up the goddamn walkthrough obviously, in this f95 thread you will see that 90% of the comments are people that are stuck in some level and ask how the hell they should progress, this shows you all you need to know about the tedious level design.
Porn:
At the start you can only have H-scenes with her in the safe rooms only if you have that red energy drink thing, which encourages you to farm resources and use the vending machine to buy red energy drinks. The girl is a virgin, so after the intro when you meet she now depends on you to inject sperm in her to avoid her turning in a monster, as you have more and more H-scenes she gets more degenerate and horny, this is a pretty bare bones corruption system. The H-scenes are fully animated and well made definitely, pretty much the only fun thing in the entire game. As she gets more horny, she will want to have H-scenes in all the hiding spots in the levels, there you can hide and fix her progressing infection for free, no more grinding for red energy drinks, which is fun. When you beat the game you get the entire gallery unlocked.