Very simplistic and fun. Wasn't quite challenging enough for my own taste and I played through it relatively quickly.
Defending your base is a cool idea, but a lot too easy at the moment. I wonder what would happen if delta spawners would keep spawning triangles so you need to pay attention to multiple triangles at once. That would make it quite a bit harder to protect your base as you always rotate all deflectors at once and that additional difficulty could just be compensated by slowing the game down a bit. Might be interesting. Maybe you can try that out.
Overall good job! I enjoyed playing it.