Been done
Good job but this has been done several times.
I wrote code for the exact same game over a year ago to see if I could make a better version of a flash game that copied another flash game. I can't believe you think this is a new idea..!
Mine actually shoots. I'll probably finish it up now and submit it just to show you it's not a new idea.. This isn't to say you shouldn't make it. Yours could be awesome but it's nothing new.