Simple but fun tower defense game. The difficulty is too low, I was tempted to stop playing after some waves, because I always had energy spare and the enemies never progressed to far, that takes the tension out of it. And it somehow stopped after 16 waves (no new enemies were spawned, but I still could create and destroy turrets).
I like how you have to balance between strong and fast turrets to get the smaller, faster enemies, that hide beneath the big and strong ones and try to pass unnoticed.