Very cool experience and great concept. The gunplay is very punishing but I think there's absolutely a market for this type of game. The visuals are great and the combat feels extremely intense and rewarding. I think the early game might be a bit too difficult for new players overall but that's something you can continue to balance over time.
Input:
The controls were kind of strange and some actions required bizarre combos. Let me right click to aim, g for grenade, v for melee, etc. C to pick up grenades is weird and shift plus double left click to throw is really cumbersome. Shooting while sprinting would also be nice.
Audio:
The directional audio seemed too extreme. I like the effect but something just off center sounded really far to the side. Character footsteps have a weird echo even in open areas. No footstep audio while sprinting in the early game but it seemed to work later on. Solider footstep sounds are overwhelming. Music stopped in some areas but there were no atmospheric sound effects to make the environments feel alive.
Camera:
The manual camera zoom felt kind of unnecessary and zoomed in/out too slowly to be that useful for me. Different zoom levels also seem to have different image clarity. The camera panning also needs some work. I didn't use it very often except by accident.
Gameplay:
I think the cover mechanic is great but it still felt a little clunky. I don't really know how to improve it but I sometimes felt like I should be in cover but still got hit. Maybe it's just a readability thing. Enemy cover usage also felt just a little off and suppressed enemies could sometimes still shoot me. The AI in general needs a little more attention. They never tried to flush me out of cover and trading shots back and forth felt a bit random. Maybe I'm missing something though. Ranged shooting is trivially easy compared to close range.
Getting a second character to control was kind of awesome. I didn't think it would work but after a few tries I could see why you added it. I never won a level if my buddy died so I don't know if there's revive or any kind of combo abilities but I think those would both be cool features. Multiplayer would be truly amazing but I don't know how much effort that would take.
Bugs:
I'm on an ultrawide and the first time I played the game was all screwed up. It seemed to resolve itself after I reloaded the first checkpoint. I had a few cases where multiple prompts covered each other up. The game crashed to desktop twice when I told my teammate to hold. My teammate entered a state where he couldn't shoot (not related to hold fire). I had a reload bug that wouldn't let me complete the reload. I also experienced some input bugs with holding left mouse to shoot sometimes not firing on release or staying precise after releasing the button.