Not great, not terrible
There are at least two immediate shortcomings that need to be fixed for this to be a great game.
First, upgrading the gun affects appearance only. You are still left with the same firing style and number of bullets. This should be different for each gun.
Second, the aiming system is not user friendly. In the time I played this game I was not able to figure it out (if it’s even possible) even with the game’s brief instructions.