Such cute walls! I don't want to shoot them! I liked that literal interpretation of the theme :D
At first I thought the gun could be controlled with the mouse and I'm wondering why it doesn't work properly. Then I realized the auto-aim. I would like to have the player control the aiming, it would give more things to do.
In top-down games, it is good to create some kind of texture or landmarks in the game area, so that it would be easier for the player to understand the effect of the movement.
The music was great! It would be nice if it's looped.