Thanks for all the feedback, I really appreciate the bug report and the suggestions (the one on the damage feedback is really on point, will surely add that and a low battery alert asap.)
On this one "every time the sub went too deep the nautilus creatures started getting aggroed from all the way across the level in large groups. Not sure if intentional.", are you sure this was tied to the depth? I have not coded it like that although I have seen they can sometimes swarm at the player randomly, they are aggroed when you attack them or if you go to close sometimes.
I think part of the charm of the game is to navigate the underwater physics (hint: if you feel like you're bumping into enemies a lot, stunning them with the stun gun makes them give you no damage upon collision.)