I also got an invite today in what i assume is a wonderfully petty move against the shitshow that is Stadia Launch. I played a quick few games before i have to get ready for work, will give it a proper go later. I went to 2 of my most played games so i could compare it: Killer Instinct and Ori & The Blind Forest.
First off, i'm amazed it works as well as it does. You can definitely feel the slight delay, especially when you have that muscle memory to go on from playing it locally. Because of that KI, while very playable, just felt a bit "off". That game, as you can imagine from a fighting game, has some very precise timing needed for things like combos and combo breakers. I would react to stuff in the same way that i was used to on console and it just wasn't quite fast enough to have it feel like a local gaming experience. In that sense it's an interesting concept but not one i would want to try again.
Now Ori on the other hand is a bit more forgiving and in that game i got used to the slight difference in the responsiveness of the controls. I was happily dashing around the world doing my thing and this is the kind of game i could easily see myself playing on Xcloud. You do sort of automatically adjust to the experience. While obviously if i have the choice of playing it on my phone when my console is right there, well, that's never going to happen. But i tell you what, i'm due to go visit my parents soon where i normally need to bring a laptop full of downloaded TV to watch (or my Switch) but now i will be able to happily be able to take a 50+ Xbox library with me and that is going to be a godsend.
There are certain slower paced games that i could easily see myself playing on my lunch break perhaps. And something like Sea of Thieves i can tell would work great with Xcloud. From my brief first impressions its surprisingly good, especially considering it's in beta. I will personally always see this as an additional way to access my games library, not my main method, even so i've gone from being vaguely disinterested on the idea to strangely excited at the potential possibilities. Never thought i would say that.