This is, by far, the best single-player game that I have played in recent years. The game allows you to freely explore a solar system in a spaceship, providing you with no guidelines and no clear goal. Essentially, you make your own goals. You find clues; follow them to another place where you then discover more about the civilisation that came before you.
The game's art style, sound design, and music are all major contributors and I strongly believe that Outer Wilds has one of the best soundtracks of all time. The music is used sparingly, only audible when you find something significant. Even then, the music is often drowned out by the sounds of the planet you're currently on. It's a really good way of using music, and I wish that more games did the same thing.
The time-loop mechanic is done in a unique way and, most importantly, it works well and is relevant to the story. I never once found it to be annoying and the game never felt repetitive at any point. The story itself is absoutely beautiful, but in a heart-wrenching way. I won't spoil it, because if there's anything you want to avoid when playing Outer Wilds, it's spoilers. From the very beginning of the game you have all the means necessary to complete the game. You just don't have the knowledge. All the text in this game is valuable, there is no location that is useless or boring and the game manages to keep you interested in something the whole time. Whether that be finding new clues, following old ones, stumbling across some new ruins or finally figuring out how to reach the end. I think that because of this, reaching the ending feels amazingly fulfilling, yet also sad.
I would highly reccomend you play this game, especially if you're looking for a new single-player game to spend time playing. This game is more than worth it. I hope this review helped (I tried to avoid spoilers, hence why it might be a tad vague). I implore you to experience this game for yourself.