Subnautica is a survival game set entirely underwater on an alien ocean planet, and it is the best in its genre at making exploration feel like something.
You crash, you survive, and you go deeper. That is the whole structure, and the game trusts you to work it out with almost no direction.
What makes it work
Depth is the progression. Everything you build, from the Seaglide to the Seamoth to the Prawn Suit, exists to let you go further down, and the game gets darker, stranger and more hostile as you do.
There are no quest markers. Progression comes from scanning fragments to unlock blueprints, and from radio messages that give you coordinates you have to navigate to yourself.
The scanner is the game
Every fragment you scan unlocks a recipe. Wandering past wreckage without scanning it is skipping progression.
There is no map. You place beacons and remember landmarks, and players who ignore beacons spend most of the game lost.
Fear, and whether that is a problem
It is genuinely frightening in places. The Leviathans are large, loud, and the sound design gives you plenty of warning before you see anything.
A meaningful number of people cannot finish it for that reason. There is a creative mode with no hazards if the survival layer is not what you came for.
The story
There is one, it is good, and it is delivered through wreckage, audio logs and abandoned bases rather than cutscenes. It resolves properly, which is unusual for the genre.
Where new players struggle
Going deep too early, without depth modules, and losing a Seamoth to something that lives at 400 metres.
The other one is oxygen management. Turn back at half your air, always. The trip out is the same length as the trip in.
Below Zero
The sequel is smaller, has more explicit narrative and a named protagonist, and is generally considered the weaker of the two. Play the original first.
Time commitment
25 to 40 hours for the main story. There is very little padding.
Base building
You can build habitats at any depth, and they serve as staging points, storage and somewhere to breathe.
Structural integrity is simulated. Go deep enough or build wide enough without reinforcement and your base floods, which is as alarming as it sounds. Foundations and bulkheads exist for that reason.
A well-placed base halfway to where you are working saves an enormous amount of travel.
The vehicles
Seamoth for speed and shallow work, Prawn Suit for depth and mining, Cyclops as a mobile base you can take almost anywhere.
Each needs depth modules to go deeper, and the Cyclops in particular is a large investment that changes the back half of the game.
Modes
Survival is the default. Freedom removes hunger and thirst. Hardcore is permadeath. Creative removes every constraint.
Freedom is a legitimate way to play if the resource management is not what you came for, and it leaves the exploration and the story fully intact.
Guides
The builds guide covers blueprint priorities and depth modules, and the walkthrough gives a spoiler-light route through the biomes in order.
