Simple but fun.
I liked this game; graphics were good, gameplay was simple but fun. Did I hear a couple of sounds from X-Com Interceptor? If so, good choice. ;)
The two things I didn't like were that it was kind of slow, and it took a long time to get upgrades. I think both these problems could be fixed if you added more enemies. It's kind of boring to shoot three enemies, wait, shoot three enemies...if you had say six or seven, or even ten, that would be interesting. In the later levels the enemies speed up, which makes it harder, but not less boring! Oh well. Good work, it just needs a little bit more tweaking to be truly excellent. ;)