It's easy to talk about the brilliant puzzle design of Outer Wilds. It's a metroidvania of pure information. It runs about five layers deeper than you expect even after you realize how deep it runs. You begin as a naive newt; you can explore in any direction; and when you have all the pieces of the story, you also know what the game's goal is, and how to get there.
One hears less about the game's thematic unity. But as much thought went into the story's symbolism as its puzzle structure. They're both necessary and they build on each other. Outer Wilds wouldn't be compelling if it were just a barrel of puzzle mechanics. So let's look at the flip side.
I already wrote the non-spoiler review. This is the spoilery discussion. Seriously: all the spoilers for Outer Wilds. Do not read this post until you've finished original game and the Echoes of the Eye expansion!