Sad I didn't have someone to play coop with, but props to you for making it a feature!
I really like the submarine side to side animation, it's simple but really clean. Also I loved the bubble gun, I thought it was much more creative than traditional shooting and wish it wasn't replaced after the tutorial.
Controlling the ship and where you were shooting was unnecessarily difficult, I assume you did it to add more challenge but the game was already hard and taking control away from player hurt the experience. I wish you could just have the sub shoot where your mouse is pointing.
Anyways it was overall fun to play, nice submission!