now listen up
This game was really really good. your choice of music was up there. Also your staging and timing was really good too. So this is my suggestion,"get an artist to help YOU!!!" I'm saying this not to be insulting, but you need to know where your talents lie, and so far i see its from the programming aspect.
If you had an artist to help you then you could worry on how to better tweak the game.
in my opinion, in a shooting game , a target should have three animations, the moving around, the attack and the death. targets shouldn't simply dissapear when you shoot them.
These are just my suggestions.
keep up the good work