Wow, very innovative game! I love tower defence, and one common complaint I have with them is that a lot of times you just shit back and watch, but here you have to be active constantly. I made it to 160 seconds, the best strategy I found was to park the four corner turrets to good areas, and focus on the middle one. The music choice is also great.
Very fun experience. I could easily see myself playing a full version of this.