Fantastic graphics and atmosphere. I'd pay to play a larger metroidvania-style game with these aesthetics.
That said, I found the movement a bit slow and clunky. I get that it's underwater, and it's fine to have that in portions of the game, but I don't want to feel like I'm swimming through honey for the whole game. The hit box boundaries of your mech and the obstacles and enemies are not very clear due to the size and complexity of the sprites. And combat was quite simple so far.
So this to me feels like a promising prototype for a much larger and more fleshed out project.
I don't want to sound too critical, I just feel like what you've got here has the potential to be a full paid game.