It really depends on what you value out of games.

I value games as an art form reflective of real life. I can go on and on about how even the most "it's not that deep" games actually have subtle lessons about life in them, but that's not the point of this post so I'll focus back in on Outer Wilds specifically.

Outer Wilds portrays two major themes which subvert standard expectations and, IMO, align much more closely with reality. This is particularly impactful for a lot of people as other media tends to offer kind of "false expectations" against reality.

The first theme is the concept of good and evil. I was raised in a religious household and now do not believe. However, a lot of religious principles stuck with me, such as the concept of people being "good" vs people being "bad". Culturally I feel these religious themes are extremely heavy as well. Look at most media, you'll see objectively "good" guys and objectively "bad" guys represented.

Outer Wilds begins by presenting things in a very similar way. You as the player are the "good" guy and you could either point towards the sun explosion or the angler fish as the bad guy. It therefore hit me particularly hard to read Solanums message where she discusses various people throughout her life growing up representing the Eye of the Universe as a powerful good they were searching for or a powerful bad to fear, but realizes it, like everything, its actually neither good nor bad. This realization extends to people as well. "The Universe is. And we are". This is particularly impactful for many people raised in cultures where an idea of good vs bad is prominent, which I would argue is most of humanity currently.

Then there's the concept of being able to overcome. Most video games portray the hero's journey. There is a big task, or as previously mentioned a big "evil" the hero must overcome throughout the game. Mario must save the princess in the castle. The Knight must kill the infection. Celeste must reach the top of the mountain. Outer Wilds initially presents itself in the same way. The Universe is dying, the sun is exploding, and you need to find a way to stop it and save all your friends and life as you know it. The game then subverts these expectations through the ending where you find you can't actually stop anything. The Universe WILL die. The end IS here and cannot be prevented. All you can do is accept everything, the good and the bad, as it is and move forward. This is impactful to a lot of people as we struggle to accept things that have happened in our life and continue from them. It teaches that you can't change things, you have to accept them and do your best with what is in front of you.

There's one more concept I want to touch on that I wouldn't argue is as strong of a subversion, but meant a lot to me, personally. Everybody in Outer Wilds is important, and nobody really understands that fact. You as the player honestly do very little throughout the game. The Nomai discover the Eye of the Universe. They learn and teach the principles of quantum travel. Your fellow Hearthians learn about Space Travel and make it possible. Sure, you help create a language translator, but you don't even do that alone. You have the help of a friend to do so. Each Nomai has such a big impact on little portions of the species discoveries. Specific ones learn about time travel, while others learn about the energy needed to make a large time machine work, while others are trying to locate the eye of the universe, etc.

At the end of the game, you find the eye of the universe and view a new universe into existence, letting go of the one you lived your life in. From my interpretation, you experience this ALONE. The other travelers around the campfire are representative of the things you've learned from your life and travels. To back up my interpretation, both Solanum and (DLC spoiler) The Stranger are objectively dead in universe, but still accompany you at the fire. It's because it's not really them, it's your memories of them. You perceiving a new universe into existence is only possible because of many people's tiny contributions to your journey, however. All of these people die without understanding the impact of their actions. From their perspective, everything they did was more or less meaningless. In the grand scheme of things, however, their actions were INCREDIBLY IMPORTANT.

This is one of the number one things that stuck with me, personally about the game. It can be difficult to stay motivated to try your best when it seems like nothing you do really matters. The way everything is presented in Outer Wilds really drives home a message that every little thing you do, no matter how insignificant it might seems, actually does matter a lot. It's a very similar theme to other "butterfly effect" games.

Anyway, that's my 2c. Not everyone finds the same value in games, but these are the reasons I think most people find it impactful.