The best game I've ever played, hands down. The survival mechanisms and exploration of this game are really fun but I think the story takes the spotlight here. At first, the story aspect may not be as prominent; but as you go through the game, you would come across pieces of lore. It also has a great storytelling device (your AI assistant and your scanner) which makes the game unique.
It also drives home the fear of the unknown really well. At the start of the game, you would find yourself stumbling around, flinching at every noise you hear. But progressing through the game and story, your familiarity with the environment helps nullify those fears, which feels great once you experience it.