[Spoiler Alert] Subnautica is amazing! I remember the first time I discovered the huge turtle whales - it was such a surreal feeling. The world design of the game does such a good job of offering a guided exploration that feels completely natural. The contours of Subnautica's world guide you into specific areas and every area has something new to offer - it truly feels like exploring another planet.
Moreover, the sense of fear that I felt when I saw a dangerous looking creature was quite stronger than what I have felt playing several 'horror' games.
Unfortunately, I stopped playing when progressing became too dependent on farming and building - two things that I do not like. I would love to play an exploration only version of the game.