Unknown Worlds' Subnautica has been available as an early access title for quite some time and recently saw its official full release on Xbox One and PlayStation 4.
If you've yet to check it out, it's available for free on the Epic Store from now until the 25th of December.
Subnautica is a rich underwater survival game where players crash land on a beautiful alien ocean planet, stranded in a life-pod with little resources and equipment. It's up to players to slowly make their way deeper and deeper into the abyss to get craft more equipment in hopes of making it off the dangerous planet.
I played a ton of Subnautica when it was in early access, and it's quite possibly the best underwater game I've ever played. The sense of dread when exploring the cavernous depths of the ocean and discovering the terrifying creatures that await is always thrilling. Like many survival games, Subnautica doesn't hold your hand at all, so it's up to you to figure out how to stay alive.
I'd recommend Subnautica at full price, so it's a no-brainer at the hot price of free. Get it now while it's still free on the Epic Store. Trust me; you won't regret it.