Awesome Work!
I love these side-scrolling shooting games. This one is quite good. Although I have a few pointers:
-Increase the difficulty a bit. Don't make the "Bosses" too predictible. (ie Scrolls left, Scrolls right, repeat.)
-Graphics are old school. Which is great but it gets boring looking at the same few objects over and over. Add more enemies, backgrounds, maybe even item pickups.
-Weapons; include more then the ships normal shooter. Enemies could drop pick up items.
-Extras: Story might be nice. Variety of levels (ie different planets, enemy bases, not just stary background. ) More dramatic music. Maybe special boss music. Cheats. Everyone loves them. Add a stage select, hidden guns, or infinite lives codes.
Like I said the game is awesome but it can also be spectacular!