This is cool. It's really manic, yet simple I like your (4-bit? 2-bit?) graphics. Obviously the major flaw is just how much chaos ensues, but I also think that's the charm. Perhaps if you gave the player more freedom of movement Robotron-style, and slowed down the enemy bullet speed, then the chaos would be more fun than it already is. Also, definitely needs audio. I liked this though, very creative!