Hey tried your game out!
I'm liking the concept you have going here. I can see many quests and more objectives that require you to overcome hazards, maybe even get weapons to fight off creatures or something. Maybe there are different kinds of fish that give you different power-ups? Maybe the creatures like certain kinds of fish? Maybe you have to know the ecosystem and creature behaviors to be a successful diver cube? Possibilities are endless.
My biggest problem, as you may have heard already, are the controls. The jumping and movement above water is a bit too floaty, and the underwater movement barely responds if at all to keyboard commands. Specifically, when a button is pressed to return to the surface, the cube moves in sporadic bursts at seemingly random intervals. The diving mechanic works well, but I would recommend movement other than just straight down, unless part of the game is timing your downward shot?
Rough around the edges but the game is pretty cool if you work out the kinks!