Very creative use of theme. The art and sound fit together really well and I enjoyed this. Nice job!

I love the image for the title screen and the blasting off animation. I the difficulty was perfect and I like the idea of different ammo types used for different aliens.

The sound effects for the rocket ship were *so good*.  It was vibrating my headphones a bit, it sounded so great.  I don't want to give spoilers on the ending but I was surprised there!  And I liked the idea of choosing your special ammo before each mission based upon where you planned to visit.  It was reasonably challenging to beat each wave, especially the 4th wave.  One thing you can do to improve your next game is have an array of bullets that you activate and de-activate instead of creating / destroying the objects.  Sort of cycle through a fixed number of them.  That way the computer doesn't slow down if you spam the fire key.