Needs polish and originality.
You need to polish this game. The background doesn't cover the whole screen, the controls get clunky around the edges, and the general style seems like it's been plastered on, so fix those things. Sound and music would also improve it, along with a moving background, or a changing background. Be creative in making your game look good, so it ends up being a good game.
There's nothing wrong with a game like this, but billions of games exactly like it already exist. You've got to make yours stand out somehow. Try making a variety of ships, a variety of weapons, maybe even a limited supply of weapons, or some other feature that makes your game different than all of the others, otherwise, what's the point of making a game like this?
Well, I suppose there is the point of gaining experience and whatnot, but if that's the case and you only made this game to get the experience of doing so, why submit it to newgrounds. Why not develop a game that people actually really like and care about? Next time you submit a game to newgrounds, try to make it a game you think people would actually enjoy playing.