It definitely has its pros and cons, and it all comes down to your specific gaming pattern and situation. If you already have a gaming pc or console, this may not be for you.
Sarcasm aside, in the longer term there is probably a business model here where anyone who wants to play a subscription game like World of Warcraft signs up and gets a $100 tablet sent to them for free.
There also might be a model where very high performance rendering combined with ML does stuff where the consumer would otherwise have to pay thousands of dollars for. Not sure that would work in an AR-VR - competitive gaming future.
I saw a demo of Stadia in person a while ago. It was ok, but hardcore, competitive gamers aren’t going to accept the latency gap.
If Stadia got EA Sports to publish NHL, I'm sold. The end to end product experience is just going to be miles better. I imagine certain games unlock Stadia for certain people.
edit: sorry slowpoke here replying to himself: I get that you are "renting" a gaming hardware for that price, so you don't need to own a gaming computer. So at $120/y it is not bad, if the service is as promised. And then if they shut it down in 3 years then, you spent/lost $360 toward a gaming device. But what happens to the games you purchased? How about renting the games also, like an additional gaming subscription?