I have now played this game through once on Adventurer, and twice on Survivor. Here are my thoughts.
Since FarSky is tagged as "survival", "adventure", "indie", "sandbox", and "crafting", I'm obligated to compare and contrast it with Minecraft, which I also have played extensively. This game is not Minecraft. Its crafting system is much simpler. It has a goal, whereas Minecraft does not. It has an end; you can "win". The randomly generated world, while being large and immersive, is finite. The movement mechanics are much different as you're under water. The terrain cannot be deconstructed, but minerals can be mined from it.
The graphics are relatively simple, yet work quite well. All the plants and animals under the sea have convincing movements. The enviroment itself is very well done, between the day/night cycles, and the way it fades into a blue haze at a distance.
The game mechanics were fun. I could get around without any trouble. The combat system is not overly complex. It can be difficult, especially at night in the first days of the Survival mode, but becomes effortless later on.
The premise is that your submarine broke into 9 pieces during a dive, and you are marooned on the bottom of the ocean floor. You must survive, equip yourself, and find the 9 pieces of your submarine. Once you do, it will assemble, and you can ascend to the surface, thereby winning the game. The game itself is relatively short. I have been everywhere, done everything, and beat it 3 times, for a total of 25 hours.