The graphics and music are nice.
There are lots of bugs, like being able to select multiple items in the shop, or 5th crab not spawning.
I'm not enjoying this format. Controls are very floaty, weak weapons, useless equipment by default, little damage feedback and getting damaged by stunned/dying enemies. You should make an actual level to guide players how to play if there's an intended combat scenario. As it is there are better ways to do submarine combat.
Best part for me? Literally the bubbles, no kidding. Those tell me the location of the enemies outside of my vision range and that's the design direction which I would expect from submarine combat that would work in 2d.
Sometimes I failed the mission but I'm not sure how, I'm pretty sure time didn't run out.