I liked the art style, the sub, the environment. Good use of dithering. However I think the lighting sort of hinders the gameplay, I wanted to explore and see the ruins, there are cool elements and rooms in the environment that I wanted to explore. Also I was picking power ups and I don't know what they were, I thought they reloaded spears or mines but that wasn't the case.
It's a cool base for an exploration game! A good entry for the jam. The shells are nice but if you want to continue developing the game I'd focus more on the exploration, the rooms, a minimap, could even be sort of like a roguelike with different rooms and objectives.
Also voice acting, so +1 on sound just for that :-) good job!