Making a point to leave comments on games I play since it sucks when no one leaves feedback on your game. Looks like this game was made a while ago so your probably not working on it but below is my initial thoughts.
1. should display the controls somewhere when the game first starts as I wasn't sure at first.
2. would be cool if you added some audio and particle fx.
3. Some type of scoring system and time tracker to see how long your survived would be cool
4. Particle fx when shooting and destroying enemies.
Anyway good job, hope your still coding..
Tom