Thought I would put up my initial impressions.
I think Google Stadia is currently more of a "proof of concept" than it is an actual marketable product at this time, and I think that is about the fairest thing I can say.
Does it work? Yes ... surprisingly well. When I first hooked up my Chromecast Ultra to my TV and started playing Destiny 2 I was taken aback at the lack of any discernable significant input lag - the quality of the image and the framerate. I had major concerns having experienced the likes of Steam-Link and PS Now previously and found them wanting. My initial impressions of Stadia were good. But ... after a short while, a few problems began to surface. After about 30 mins of playing I noticed my TV switching to a different resolution and the framerate clearly dropped. I restarted the game, but to no avail. I restarted the Chromecast Ultra, and that seemed to do the trick. This time however, there was a 3 second delay in audio. Everything else was running smoothly for whatever reason .. just the sound.
I played on like that for a little while, and then again - the quality suddenly dropped for no apparent reason as did the frame-rate. I should add, this audio-sync was not just with Stadia - it was happening with all streaming through the Chromecast Ultra (such as Youtube etc.).
Everything else about Stadia seems bare bones to me ... a basic/minimal UI that lacks features you would think important for a streaming service ... the controller, whilst comfortable to use, to my mind feels cheap in comparison to its rivals. Trying to play Stadia at this moment through the browser seems pointless, considering the poor quality (as it is at a lower resolution for now).
As a product, it is a hard sell - "buy our Chromecast, buy our controller, buy our subsription and then buy the latest games at the same price you would pay for if you had a PC/PS4/XB1 etc.". Honestly, unless this model changes, I think the market will probably reply "Nah, your alright, Google ... good luck".
The model needs to change, or at the very least the subscription needs to offer more - imagine if a Stadia subscription came with something similar to the Vault Access with Origin? Suddenly, you have something more marketable ... Something like what XBOX may well be offering in the not too distant future.