Very nice game idea.
I did have trouble understanding the mechanics though.
When entering a fight it start with the gun firing then we wait for mobs to show up, then we type as many keys as we can before timer runs out which does not deduct any bullets or have any gun animation. When the timer is near the end you are locked from entering keys so you kinda need to upgrade the timer so you got additional time. When you get to the boss you shoot automatically without entering a key. Had to spam a number and hope it would end up at that number to kill him, was this intended?
If these things was a bit clearer it would make the game even better.
Good job!