Simple but fun. The narrow corridors make for a tense experience.
You need to mention that the game uses mouse to aim in the game's description.
I think the hit a single wall and you restart thing kinda kills the momentum. It'd be better if the player is penalized less. A more complicated scoring mechanic that penalizes you for knocking into walls would be better. You could also let the player richochet off walls.
Another huge improvement would be to remove the reloading and make it like Celeste. In this case, it is simply disabling the collectible, enemies when the player take cares of them and reenabling+reloacting them upon respawn.