Shoot 'Em Up Prototype

Hello, this is the first version of Excalibur-85. Been working on it the past three days, I have the core mechanics created and implemented, but far from refined.

You have a shield and hull strength meter. At the moment there’s no way to replenish your hull, but 2 seconds after you either deactivate your shield or it’s destroyed, it will begin to regenerate quite quickly. While the shield is active it will not regenerate. Projectiles can collide and destroy each other, and if they have enough durability left they will pierce more than one enemy. There are four enemies in the game, three “waves”, a new wave begins 60 seconds after the last.
For now the third wave lasts indefinitely. There are no graphics or sound in the game, all graphics are rectangles generated by the code. I went this route so that I can worry about fleshing out the gameplay before I start on the art direction.

Controls:
Press or hold U to shoot.
Press I to toggle your shield.
Movement is WASD or Arrow Key based, whichever is more comfortable for you.
Press Escape to close the game.

If you try out the game and feel like giving criticism, I would appreciate you taking the time to do so.

http://s21.postimg.org/jll9yhdqf/screenshot.png

http://www.filedropper.com/spaceshooter