This was fun! I liked dropping trees and rocks on enemies. It took me a while to figure out the turret and tower building process, but it then clicked for me.
I found the mouse controls to be a little tricky. I would like to play that way, but the copter has a ton of inertia. Could you maybe set it so that when you click a spot, the copter will get there and stop there dependably?
Very cool game, and very creative use of the assets! Nicely done.