Somewhat fun game. Rather repetitive, but no more so than the average mid-'80s arcade game. Could do with a steeper difficulty curve though as it's a little easy and as such gets tedious waiting for the harder levels...
Good job on doing the game, it's enjoyable, I had fun, but it's indeed a bit basic (lacks sounds, better shooting, increased difficulty curve etc...). Keep it up ! :)
If you are looking to improve it, I'd start with collision and shooting. Calculate them from the front of the ship so it's more realistic.
Good game