Fun to play! The bad graphics are no problem. You could replace them in some hours with great assets.
Some ideas for improvements from:
- your bullets that hit the enemy should instant remove or explode or what ever and not fly through them
- If an enemy hit you it's hard to run away and it kills you very fast if you don't run in the opposite direction. You should add a time to be invincible after hit for a second.
- The enemies should have some health indicator.