The downside is that it has very little replay value (you can beat the game within 5min if you already did before), but the path to get there is difficult, engaging, and extremely rewarding.
It's difficult to describe Outer Wilds, but I'd put it as an "open-world Portal", only it has numerous Portal-like quicks in itself.
There's a unique in game language (and a good, and then really good hint in the game on how to crack into it); but it is _not_ required to even get the good ending. Just enough of the lore's surface is there and a player still has a good chance of reaching the good ending. All the more so after seeing the bad and then reloading the save file (standard game mechanics).
Some fans have even put together decoder tables to assist translation of the game language to English; as well as a version of the manual that's completely translated if you don't have the time or desire to do that.
Or maybe it’s a distinction without a difference. I know I’d rather see more Outer Wilds games out there than more Skyrims.