Really cool concept! The first second I was confused, i am using the arrow keys to rotate the gun, so does that mean I cannot walk around? This seemed a little strange to me, but then I shot the gun and saw the knockback and I understood. Really clever mechanic, because you cannot shoot and walk in the same direction.
There were a few issues, like once an enemy would spawn on top of me, which made me lose immediately, or enemies would spawn outside of the level area. Another is that sometimes enemies spawned very close to me, which did not give me enough time to rotate the gun towards it to shoot it. Maybe you could check if a spawnpoint is a certain distance away from the player? Or maybe add some effect where an enemy will spawn, so that I can run away from there as the player?
Great submission! I really liked playing it! It was also cool that I could shoot enemies from halfway across the map, for some reason this felt really nice :D I agree with J.Anthracite that it feels like there is potential here and you could continue development if you want to :)