Thanks for your comment and also for the video, it's a great feedback system!
I completely agree with what you say. We had ideas for several complementary mechanics during the gamejam, such as: more complex level with keys to find and doors to unlock, oxygen refill scattered in the level, and even a harpoon gun to defend yourself from nasty fish.
However, time was running short. I spent a lot of time on the basic mechanics (movement, water, loots) and didn't have enough left to implement anything else.
I don't think I'm going to continue developing this game, but it gave me ideas and allowed me to experiment with tension/time limit mechanics, which I intend to integrate into another project I'm currently developing.