Really cool control system! Moving and shooting with the mouse felt really nice. I love progression systems, but I think you need to balance the cost to enemy drop value for the various upgrades. The enemies are a little too simple in the beginning, but your low power level makes them take a relatively long time to kill. And the fact that it takes at least two rounds before I can buy any upgrade makes the opening drag a little too much. But if you iterate on these values, I am sure you can find the right balance to make this game awesome!