Great game !
Few more levels would be great but 72 hours is not a lot I guess.
The only thing is that you sometimes have no time to activate the bullet time before the bullet hit the ground. I would have appreciate a way to anticipate the firing. Some kind of red light on the gun that would flash 1/2s before firing.
And a way to understand that shields are destructible (they could shrink of flash when hit). At first I thought that shielded guns were not to be destroyed, but avoided.