I would have a suggestion:
Could you make the shooting possible by pressing any part of the screen? Then this would be playable with just one hand. I think it is a bit unneccesary to press the screen where you are shooting because the character always shoots in the same angle and the direction (left or right) is adjusted by tilting the phone. Also, could you make the random level thing a bit more random, I got the red planet stage ten times in a row?