I really liked this game! I felt the controls were responsive and the premise worked really well for the theme. I also enjoyed how the asteroids could destroy the enemy ships. I think that worked very nicely and added a lot to the game feel.
If you wanted to improve, I suggest not allowing the two ships to overlap. That made the game a lot easier and made it so it was easier to have one ship that fired twice as fast. My suggestion is to have one ship not fire if the other is in front of it.
Overall fun game!