This was a neat tower defense idea. I loved how you could switch between the worlds. My only feedback is that it seemed too easy. You've got a lot of the groundwork for a more robust game. If you plan to take this further, I would think about how you can add strategy and player choice to the game. Right now my only real choice is which soldier to deploy, and even then, the money ticks up so fast, I may as well wait for the most powerful one. If you expanded it so that there was more than one plane to place your fighters (and for enemies to attack), it could add some strategy to it. Great job with this one!