Google announced the pricing structure for Stadia today and it's...weird. You pay a monthly fee for access to the service BUT you also have to buy games just as you would for any other console. Netflix for games this isn't.
Ideally, this service would have allowed you to pay a monthly fee and play any game available for it. You would only have access to these games while you're a paying customer. Even at $20 a month, it could be a worthwhile service if the game library was attractive enough.
Instead, it's more akin to existing digital game structures. You currently have to pay a subscription to access online multiplayer features on all consoles but you still have to buy the game up front. Stadia's intent seems to be to simply remove the console from this situation. You buy a cheap controller and a Chromecast or similar device and you're ready to play. There's a lower barrier of entry than current consoles but only in the upfront costs for the hardware.
Will it be a success? I'm less sure of that now. Without a huge differentiating factor to existing consoles, there's little to draw hardcore gamers. Would casual gamers even want to pay a subscription fee?
The only hope I see for this is if Google can churn out unique experiences that are only possible on Stadia. With the incredible amount of cloud computing power behind it, Stadia can offer experiences no console could. If enough of those experiences are attractive enough then Google will have an opportunity to convince anyone who checks it out that the rest of Stadia is just as good or better than their current online services. But I'm sceptical we'll get those experiences.