Overall, with no resource mechanic to speak of, this felt like a "click as fast as possible" game rather than a more strategic one, which is what I was hoping for. "Tower defense where towers surround the player" is fun -- which is how I thought of this game -- but not a "GENRE, but without MECHANIC" match very well. Interesting game, but really would like to see it as a strategic, rather than "race" style game.
Also: Support WASD. Your weird Q/Z/S/D controls were confusing. (The arrow keys were fine though.)