DEPTH CRUSHING

The flora and fauna that inhabit the depths seem to defy the scientific status quo. Creatures too large to exist, ecosystems that resist multiple mariana trenches worth of pressure, new molecular compounds never before seen. Corporate greed has found its new frontier.

Every industry in the galaxy is interested: From Cutting-edge pharmaceuticals, to secret military developments, to femto-scale-electronics. The oppurtunities are bottomless and the competition fierce.

They just need somebody to do the hunting and gathering.

Fight your enemies with high-skill fishing expertise combat inspired by the Souls series and Sekiro in 6 degrees of freedom. Turns out, underwater, sometimes it's better to go melee, with many different unique spears, swords, hammers, and other hunks of metal to choose from.

Use materials you harvest to gamble/craft for unique weapons, perks, consumables, and more. Each dive is procedurally generated, and your success is defined by your mechanical combat skill as well as long-term strategy. 
Couple this with Survival-Horror resource management: Tech breaks down in the abyss, and everything is limited, especially the oxygen in your lungs.
AQUATIC ENVIRONMENT
A soundtrack with only two moods: prog metal and aquatic ambience. 

A dreamy PS2-era artstyle to induce the aformentioned thalassophobia.