The concept of the game is really good, they certain things that can be made better: not everyone has a gamepad availabe, one solution to this would be to use the mouse with click to move and right click to shoot were the mouse is or use the arrows keys with numpad for the second player. The UI was a bit too big, the boss health bar can block where the player is, you can solve this by having the zoom out to be slightly bigger to make sure that it won't ever block where the player is, but overall the game is pretty good.
I have seen the other comment made by "CoolLikeGoose", hope you are doing great after your comeback to Unity and continue to doing great afterwards. :D