I don't know if you guys plan to update the game, but here's some feedback:
- Mood of the game was well done.
- Controls are a bit confusing. I would have gone for W-up, S-down, A-left, D-right and I also thought that I was supposed to return back to the surface.
- It states new game instead of continue on the main menu, after you have already played the game before. Also the buttons on the main menu are really small.
- You can only pause on the surface and not underwater.
- The energy just decreases at a constant rate regardless of whether you move normal or turbo or not at all.
- Instead of having a narrow area underneath the boat were the objects spawn on load, spawn objects around the submarine (outside of the screen) depending on the depth. You can also just move outside of the area, avoid all the enemies and get to your desired depth.
- When flipping, the sub and torch flip seperate from each other. Also you can "dive" to a positive depth.
- There was no win screen or something, when you dare to buy the upgrade.