Thanks for the feedback.
"My advice if you want to try another fps, more walls and cover would be nice as well as some guardrails to shield from the precarious bottomless pits so the player has the option to retreat somewhere they won't be shot at from all directions (the fifth and sixth levels are the biggest offenders imo)", I'll add this to my next fps.
"Also, if you want the guns to have infinite ammo, make them behave like power-up pick-ups instead of letting them all be used at any time against any enemy because there's no incentive to use anything other than the machine gun aside from the long weapon reload times", I tried to implement this, but it was a bit complex and we were short on time, so had to leave it as it is.
"I do also think it's weirdly redundant how unlocking cages requires keys but the player is given all the keys they need right at the start and never needs to collect any in all of the levels", didn't get you there. In the start of the level, player has 0 keys and has to collect keys by killing enemies.