Very creative interpretation of the theme! One way you might spice things up is by making enemies hurt the player on contact, making traversing to towers to wind them up more difficult. In generally winding up the towers got somewhat monotonous. Maybe instead of dropping so quickly you could overwind the towers if you constantly crank them to temporarily increase fire rate. Also, a next wave button would be a great quality of life improvment. Great concept and execution. Plus I love that wind up sound!