This is a great small defense game! You implemented the towers functionality really well and the waves of enemies provide a good challenge. The mechanism of using the cash to build the towers is really well done, though it can be a little confusing. I would maybe add some more feedback text for the user. I like the mechanism of placing the towers where the player moves to, so the player has a lot more freedom with the placement. Maybe add some "platforms" to the ground to give the player some structure to the placement. Overall, a great game! I can't wait to see where you go from here.