This is a nice idea and good interpretation of the theme as well. I think adding visual and audio feedback on just a few actions like shooting bullets, hitting bullets, enemy dying and enemy hitting the player would do wonders to the overall feel of the game! Another suggestion would be on the controls - I understand since its a circle that itself presents a challenge because the direction changes continuously, but it felt a bit confusing when for example you are at the bottom and you press left, the character moves right.. I cant think of a solution to this problem, but something you can think of when you are revisiting the game! Overall a good attempt though, well done :)