Outer Wilds is one of those games that is better the less you know about it. So I will be a bit vague, bit this would be my pitch:

It's a space archeology game with a very good story, charming characters, and an intriguing mystery. It has fun mechanics, as I enjoy simply flying around in the ship (once I got the hang of it) and some unique puzzle design.

After the tutorial section it is an extremely non-linear experience.

Highly recommend, don't look up any spoilers though!

Unfortunately, I agree with the other commenter. It's very hard to talk about the game without taking a bit out of the experience.

I will say that it's a space exploration game, where you fly around a tiny (handcrafted!) solar system and explore the various planets. There are a handful of mysteries around this solar system and you eventually figure out how the various clues intersect.

It's also very much a game about information. You never gain upgrades or stats or anything, your character when you start the game is exactly the same as when you finish it. But you learn things about the solar system and your knowledge of this world and it's mysteries increases, directing you on where to go next and what to do. The game also doesn't present you with explicit goals, so at the beginning you can do pretty much everything you want, but there is an ending you will eventually reach by following the clues laid out around the universe (and I seriously recommend that you don't stop before the ending).

It's also a very hard game to replay, as after you know the answer to the mysteries, there's a part of the appeal that is lost. I wish I could forget about it so I could replay it fresh!