Developer: Unknown Worlds Entertainment
I doubt anyone would disagree if you said the open world-crafting-survival genre has become over-saturated in recent years. From zombie-infested cities and frozen woodlands to apocalyptic wastelands and everything in between, we've built shelters, faced dangerous nights, and crafted gear across a plethora of locales and scenarios. Subnautica adds a new depth to the genre, quite literally, as you explore and survive in the sprawling depths of an alien ocean.
It's an engaging cycle; new equipment allows you to explore more of the world (a reward by itself), thus acquiring new and better material and having access to better gear to explore deeper. In my opinion, the fact that every piece of equipment has a direct tangible effect, from faster movement or more air, makes crafting and collecting material more tolerable than in similar games. Once you're constructing bases on the sea floor or building submersibles, Subnautica really opens up, as you establish footholds in deeper terrain.
Steam Early Access; the most recent update added a gravity gun-esque Propulsion Cannon and a Workbench to lets you modify your gear in new ways, among other content. You can follow its progress here and on the developer's Trello board.
*Subnautica is currently $17.99/10% off until June 22nd for the Steam Summer Sale.