It basically just gives you a Windows desktop you can install whatever you want in and stream games from there. It lets you use your entire investments in Steam, Epic, etc. with the benefit of a streaming service. It's also surprisingly not all that expensive (especially compared to buying equivalent hardware yourself).
It also entirely solves waiting for games to show up on these services, or going away (a la Geforce Now), and ownership issues. There's no problem even putting custom software, games, dev environments, whatever, into the Shadow machine.
I was about to buy an entirely new rig and tbh, I'm probably just going to get a Shadow subscription in a month or two.
note there may be a several month wait for your Shadow rig to be ready as they provision dedicated hardware upon subscription and are pretty popular at the moment.
https://www.theverge.com/2019/4/2/18292177/microsoft-ebooks-...
So, there's a precedent, and this leaves me a bit hopeful. OTOH, normally you can only ask for a refund if you played a game for < 2 hours
Some games are also available for free:
https://stadia.google.com/games/super-bomberman-r-online
https://stadia.google.com/games/destiny-2
The subscription gives you 4k streaming and games that you can claim and keep (as long as you have a subscription, even if you interrupt it and resume). Very similar to Xbox Games with Gold:
https://www.microsoft.com/en-us/store/collections/gameswithg...
I was skeptical at the beginning, but I prefer it to a Netflix style subscription (like Xbox Game Pass Cloud or Playstation Now)... since if the movie that you're interested in leaves the streaming service, it's not a big deal (or even if it's a whole season of a series), but if a videogame is leaving, that might be quite a bit more frustrating, since it might take you more than 1 month to actually complete your game. At least with Stadia I know that (as long as my Stadia account is active) I'll always be able to come back to the games that I'm playing now.
Just like on Windows and Luna, you can also make use of your Ubisoft Plus subscription, though (only available in the US, for now)
One nice thing is that a lot of modern games (like some available with Ubisoft Plus) have "cloud synced saves" or cross-progression. So you could stop playing on Stadia, and continue your savegame on another platform.
Alternatively, you can just buy games outright and play them whenever/wherever; no subscription required.
I have ~70 games in my library right now because I claim the Pro games each month. If I were to cancel my subscription, my library would shrink to just the ones I've actually bought (Hitman and Cyberpunk).