As a user, I'm extremely happy. I recently moved from Google Fiber (Kansas City) to Portland (Xfinity) so I was a little worried that Stadia only worked so well because I was on fiber + Google, but it's worked amazingly well out here as well.
I briefly tried GeForce Now since it's cheaper and it was fine, but I had some input stuttering and graphics downscaling that was an immediate dealbreaker for me compared to the flawless experience I had on Stadia.
To me, it seems like Stadia has the tech down solid, and the biggest downside is the game library. However, they also seem to be picking up the pace they release new games at, and there's way more games per month free on Pro now than there was months ago, so that's really exciting to me.
I play Stadia on the same TV I have a gaming PC (mostly for VR, but occasionally for RPGs with an Xbox controller), a Nintendo Switch, and an Xbox One -- and I've found myself pretty exclusively using the Switch and Stadia for the past few months.
I doubt I'll buy another game in the future outside of Stadia, unless it's something for the Switch. The Xbox is pretty dead to me now (and I don't think I'll upgrade to a next-gen console) and I much prefer Stadia over my gaming PC since I can also play games on other devices now.
I'm excited for Amazon's Project Tempo and Microsoft's xCloud, because they might be better at getting the licensing needed for massive amounts of games at once. In the meantime, Stadia seems like a clear leader in streamed gaming to me.