Cool game! I like the music and how the enemies reflect in the black water! Some nitpicking:
- Maybe add an animation when bullets gets destroyed when a boss phase is completed.
- I think it will work well to use the secondary weapon on right mouse button.
- Add some kind of indicator on the boss bar of how many phases it has, ex multiple bars, different colors or romeral numbers on one side of the bar.
- Gamepad support.