Firstly, brilliant concept! Is this based on anything? What were you influences? I'm really curious :)
Art wise, your color choices could have been a lot wiser, it's really painful on the eyes now, and this kind of saddens me, because the style in general is great, I love the rockets, but not so much the overly saturated green on the robots.
Game play wise, I love it! I just don't understand what moving back and forth really accomplishes :)