Try Harder
See, this is why the internet is practically made of graphics you could have put into a game like this. There's also this forum thing where you can ask people to draw stuff for you. It is actually sort of fun, but it looks like something a kindergärtner would put on the fridge. Fix that, and you're on your way.
For the gameplay, I'd suggest adding more guns, such as side lasers or missiles or flame throwers or whatever when you do it again.