I want start with what I liked about the game. It was very funny to see that the main character is a cube police and it rolls whenever you jump in the air. The shooting mechanic was pretty decent.
On the flip side, I can appreciate your ambition and I hope that my constructive criticism will help you in the long run, but the game wasn't that fun to play, at leas for me.
Firstly, the jumping and moving are a little bit wonky. I found it very hard to not get hit by the bullets of the enemies (you can look into more videos on how to emulate gravity into a 2D platformer. There a plenty of them). Moreover, another problem I have encountered was with the shooting. Apparently enemies can shoot through walls and vice versa. The main camera is also something that breaks the shooting as it moves away from the player in the opposite direction.
Secondly, the "Try again" screen feels to long for me. In my opinion it, would have been easier and not for the one who plays to just instantly restart the game or at least have an instant gameover screen.