Are virtual buttons being pushed? It's hard to tell in the video. For single-button shooters that don't power up weapons when a button is held down, I've always wondered why we bother to have a fire button at all. Most people just push it repeatedly anyway, and a built-in auto-fire saves finger strain.
It's not related to this game, but I hate playing games with virtual stick and button interfaces. You spend 66% of the game with your thumbs or fingers covering 66% of the screen. I think it sort of defeats the purpose of the touch screen. Time to come up with a new interface paradigm. :-)