I usually don't like games where you can only shoot forward, but this one was quite addictive and fun - good job! The variety of power ups, enemies and special weapons made it interesting, and +1 for the light humoristic attitude.
It was a bit disappointing that after 3/4 of the game or so, there were no more new enemies and the upgrades made it too easy. I replayed a few levels just to try the remaining special weapons I didn't need... A bestiary would've been nice, too. And there's the ubiquitous little annoyance that you can't silence sounds or music while it's paused.
Well anyway, I'm definitely waiting for this one to be continued :)