As spaceship Aurora is about to crash onto an alien planet, you find yourself on an escape pod and land in the ocean, where you begin your quest of survival. After quickly putting the fire out in your pod, you can go exploring, returning to your pod which acts as a temporary base. The Fabricator there can craft many tools as well as cooking the fish you catch.
Luckily, the Bladder fish are found swimming near your pod, which will become your source of drinking water, and many of the smaller fish can be caught for food. Apart from this, you will be searching for scrap metal, and ore deposits, and trying to locate blueprints in order to craft tools for survival. There are tools like a knife, flash-light, cutting tool, fin, tank, helmet upgrades for your scuba suit.
Eventually you will be building a base for a more habitable location. Building a base can be very clunky. It's not obvious what the criteria for placing buildings is. Often, I was sure I should be allowed to place a building in a location, but the preview would be red, telling me I couldn't place it but giving no reason why. The bases you build can feature all kinds of cool features thanks the the “habitat builder” tool which is like a futuristic 3D printer.
A Scanner Room can highlight points of interest in a certain range (wrecks, ore deposits etc). The Moonpool can dock your small vehicles, recharging their power. There's a Water Filtration, Battery Chargers, different ways of generating power like Thermal Reactor, Bioreactor, Nuclear Reactor. There's all kinds of objects purely for aesthetic purposes; so you can create a bedroom with cabinets, shelves, plants, and pictures (using in game screenshots you take).
As you play, you will receive radio transmissions which lead you to certain locations like other escape pods. There you usually find a blueprint which helps you progress further, so following the story keeps you progressing at a steady pace. Later on, there aren't many transmissions to guide you, but you do find more back-story of the island, and then you have to find a few underwater bases.
The world is really beautiful which makes it a joy to explore. Although venturing down into the darkest depths can be rather scary; it is the ocean after-all. The deeper you go, you are more likely to find more aggressive creatures and plants. In certain areas, Leviathans make their home. These are really scary when you first encounter them. Sometimes you know they are coming when they unleash a mighty roar, but other-times I found them being a bit more stealthy. Once you get used to their locations and behaviour, I didn't find them daunting and was good at avoiding them.
To reach the deeper ocean, you will need to upgrade your tank, and create submersible vehicles. The basic “vehicle” is the sea glide which is a motorised device you can quickly pull out to travel faster. The small vehicle you make is the Seamoth which is a roundish submersible with a small storage capacity. Initially, it can't go very deep, but can be upgraded to reach far deeper areas. The Prawn Suit is a mechanised walker, with jump jets which gives you the options of walking along the ground, or travelling longer distances. It has arms which can pick up objects (and automatically place them in it's storage) or punch creatures. The final vehicle is the Cyclops which is a huge submarine which acts as a mobile base. It has high storage capacity and can dock one of your vehicles too.
There's no in-game map, so often it is really easy to get lost. Apparently, there is a Beacon blueprint in the game but I never found it, meaning I could only use the compass, and beacons emitted from the other escape pods to get my bearings.
To reach the underwater bases as part of the story, you need to venture to some underground caverns which there are only a few entrances to. You don't seem to get many clues where they are, and the underground area is absolutely huge. This part of the game starts to drag, and I found myself looking online for videos and maps, but I still found it hard to orientate myself. My advice to players is to make a list of essential items you need to make a base, and transport them down there. You will need a good supply of food, water, and Power Cells for your transports in order to explore down there.
The draw distance of the game is quite disappointing, so sometimes you find scenery popping up when you get closer to it, rather than being able to see it at a distance. Often it is quite dark, but if the ocean is brightly lit by the morning sun, then it's definitely noticeable.
I stumbled across a few bugs here and there. There were several animation bugs, a few times I'd fall through the floor, and an area didn't initially seem to load the textures. I also noticed that the lighting wasn't correct when you load a game, so was often darker than it should be (it seemed to correct itself when you move towards a light source though). The bugs were forgivable, and in general it is a well-made game.
I found the game to be really enjoyable and addictive, often finding myself playing for several hours at a time; something that games often fail to make me do these days. It takes a long time to complete though; I think I ended up with around 40 hours in the end.