Great, but it was too easy for me. Actually I could survive to the end with no single gun equipped... Like TuXiLLO says below, you could add some boss battle (maybe when the background color changes?). As for me, further update for coin attractor (like its attracting power gets bigger, or doubles coin value) or something like that would make the game a little more interesting.
And one more thing - go-back-to-menu feature (during the game) could also be added.
Anyway this is very interesting game! Keep working:)