It's a great idea, but not really executed to its fullest potential. I like this concept of diving deeper better than most in the jam, it's super fun! but I think it should have a health system or a consequence for losing oxygen. With that system , you could add air pockets and caves underwater to regain oxygen and instead of an upgrade shop you could instead have to find parts underwater to upgrade the submarine, then bringing the big treasure to land to win. Just giving some ideas of mine, you don't have to add them but either way, Great game!