This particular game remains the only title I have purchased Day 1 and at full price (30 euros), in the 20+ years that I have been using PlayStation. Unfortunately, I had to buy it digitally because the stores in Greece completely ignored it, at least when the version for consoles was first released in December and about 1 year after its release for PC, where it was in early access for quite some time.
Since I couldn't run it on my computer, I was eagerly waiting for the PS4 version.
Was it worth it? 100%. I have recommended it to all my acquaintances, and I will do the same for you, reader. With one piece of advice: Avoid any spoilers.
The only things you need to know are that it is a first-person game and single player*. The spaceship you are aboard crashes on an unknown planet, without knowing what, how, why... As soon as you manage to survive the accident and in your attempt to see the horizon, you only see the sea. Good luck!

*Single player indeed, but the only "touch" of multiplayer it has is truly amazing in conception!! Those who have finished the main story at least once understand what I mean. :) Congratulations to this small company for their masterpiece. It had been years since a game captivated me to such a degree!!

Subnautica is a Survival game where you play underwater.
You are a poor soul who had the misfortune of surviving a spaceship crash on a watery planet. Starting with few tools and an AI in your life pod, you will have to explore the waters to gather food, water, resources, and recipes to build a base, explore deeper parts of the ocean, and solve the mysteries of the planet in order to escape.

Fortunately, the game is futuristic and your life pod is equipped with a building tool that cooks and creates all the necessary tools, provided you have found each recipe, or the AI deems it necessary. The ocean floor is a terrifying place, and although the hostile fish rarely cause enough damage to truly endanger you, this game will make you fear the sea.

The graphics are good, but the game is not well optimized on all platforms. It takes about a minute and a half to load into the world (unless you're playing on PS5 from an SSD), and sometimes lags on PS4 or takes time to render details in the geometry.

Nevertheless, if you persist and see it through to the end, it is an exciting experience.
The game has received many quality of life updates since its release. If you found it cumbersome in the past, it's a good opportunity to give it another try.

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Hints for beginners:
* Don't bother with the eggs you find. They will only be useful much later in the game when you build an aquarium.
* Rocks can be found by breaking simple stones on the seabed (if you don't have a tool, they take 3 hits). Depending on the area, there are different rocks with different resources. Sulphur can be found in the nests of exploding fish.
* Debris must be scanned to find the recipe for the item it used to be. The ones you can take and convert into Titanium are different. Always have your scanner in front of you, and if you know the recipe for something, you will get titanium.
* Always carry beacons with you so that if you find an interesting area, you can tag it to find it again.
* You can catch small fish with your hands as items. The purple fish (Bladerfish) provide drinking water and don't offer much if you just cook them. Once cooked, they start to spoil unless you cure them, so it's best to eat them immediately.
* To collect sample items, you need to hit them with a knife, and to make a knife, you need Creepvine seeds, which are the seeds found on some of the large plants in the shallow areas where you start.
* If you find a useful plant in a deep or dangerous area, you can plant it in your base. If you hit the fruit with a knife instead of taking it, you will get seeds to plant and multiply it.
* If you build a large base or at a great depth, make sure to build reinforcements on the walls or platforms to stabilize it. They increase its overall strength.