Over all I liked the concept of this one and thought the audio was great. My main suggestion is agreeing with the people saying the game is a bit easy. I too was mostly able to play by listening out for the enemies and using the sonar, and so I almost never got fired at. Having the enemies try too find me whenever I fired at them, or perhaps taking the suggestions of the different speeds or limiting how many torpedos you can shoot would make it more challenging. You could also get rid of the levels featuring more stationary or not aggressive enemies, they are a good idea for a tutorial perhaps for 1 and 2 enemies, but after that I think you can just immediately give people enemies that can both move and fire.