Here is my feedback:
There has to be textures on the walls. The game looks kind of ugly right now without them
The movement physics feel weird. They feel very slide-y
The voices overlap if you go too fast
I don't know if I just didn't make it far enough, but by what I've seen is that there are no checkpoints which really killed my motivation when died
This bug:
The grenade launcher is REALLY hard to use
I died once and fell out the map while using said grenade launcher
So, I just think the game needs to be refined. While it is good for a quick mockup, I know that isn't what this is, and it pains me to have to give SO much feedback
Something I'd recommend to help is to start with fixing the physics and the audio bugs, then the checkpoint
But I code in Godot, so I have ZERO clue how hard it is to do that stuff in Unity
I hope you find this useful, good luck with your game!