Once I understood what to do and why, it became really fun! I ended up beating all of the waves and I was ready for more!! Since the player doesn't take damage (as far as I can tell?) I ended up camping by my main tower and building a ton of defense towers all around me while I hammered down zillions of foes. It probably would've looked really funny from an aerial view! A solid idea, and I could even see it being a fun multiplayer game.