What is the goal of the game? I also don't understand the movements.

This is definitely glitchy. ;-)
In the beginning I had problems grasping the controls, but in the end the main problem was that I a) confused front and back of my submarine and b) rotation is much too slow. Thanks to the much too slow acceleration sometimes I couldn't move myself. And I collide with my own bullets. All this added to the confusion.
I really liked the idea of using real drawn graphics; not sure about the choice to use lined paper, but it added to the authenticity. The mouth-generared sounds are a plus too. :-)

Neat visual style even if it doesn't quite fit the sub-nautical shenanigans. I've only seen a similar style a few times and never in a jam, surprisingly.

Despite giving it a a few goes, I could not find my way out of the labyrinth. The map is big and has no landmarks and the many obstacles populating the world don't help either. Defeating the sea chest was easy at least!

Getting the hang of the controls was the first hurdle to overcome. It is strange how forward and reverse movement speeds are both equally powerful, yet in the end I quite like how this makes it possible to zigzag around hazards.

Shooting torpedoes is not only useless, but also dangerous! Torpedoes are essentially guaranteed to come back to bite the sub or at least stir up those blasted sharks even more.

For some reason there was no sound for me on Linux. The windows version has the torpedo sound effect, but nothing else. I guess there aren't any other sounds of music. The console in the Windows version also fills up with errors… You might want to look into that.

Technical difficulties are tough and salvaging a project at the last moment is admirable, yet that doesn't exactly translate to a high score.

Overall: Bad (3.0)
Graphics: Above average (6.0)
Audio: Lacking (2.0)
Gameplay: Bad (3.0)
Originality: Average (5.0)
Theme: Bad (3.0)

I have no idea what's going on, but then again my submarine is technically a sandwich.

My biggest achievement is managing to reach some hidden place in a cramped corner with plenty of medpacks. I'll consider I won the game.

The art style is cool by the way, the game is a complete mess but I didn't mind that much, I only wish there was more of an objective to the game to make it less sandboxey.