Amazing mechanics! Very simple yet incredibly inventive, I wonder how this hasn´t been made before. The idea of the enemies creating more danger as you kill them so you can control the danger, but at the same time needing the money to buy stuff and having to kill the enemies before they disappear....I don´t know if I would change anything. Maybe I would get rid of the circle and have just the square. You could add stuff that accelerated the rotation, or which gave you two squares (double shot power but dobule the risk!) enemies that move or explode in different ways...I´m sure you´ve already though of some of these and you just didn´t have time to include them, I hope you develop this further as you can do many cool things with these mechanics!!