>On Stadia, you have to buy the games separately on top of the streaming subscription

FWIW, the subscription is optional (with these perks [1]). You can also just buy the game you want to play and play it, no subscription needed.

[1] https://support.google.com/stadia/answer/9798345?hl=en

Nvidia and Luna both took the shortcut of just running a windows VM and running the game as is. Stadia is the only one that actually requires games to integrate with its API, similar to Steam with Steamworks, and this allows them to provide a far more integrated experience, with friend lists, friend invites, voice chat, achievements, and so on. None of the other services can provide that. Well GFN does but that's just running Steam. In the short term it will slow down adoption, but in the long term the experience is night and day, imo. Being thrown into a VM instance where you have to login to Steam is nothing like pressing one button and being thrown right into a game.

Also, yes if you already have a huge Steam collection, the thought of buying games on a different store is not great, but I don't think Stadia is aimed at people with a PC gaming rig and 1000 steam games, it's aimed at people who don't have a gaming PC or console, and want to play the latest EA Sports or AAA game. Having to just pay 60$ is far better than paying 60$ + 500$ fo a console + waiting for shipping and installation.

>Nvidia and Luna both took the shortcut of just running a windows VM and running the game as is

The customer value add of anything on top of that is proving to be extremely thin. I used Now extensively in 2017, Luna extensively this year and Stadia briefly for Destiny 2 - Luna's experience isn't worse enough to provide any benefit to the Stadia lock-in model.

Stadia PM's should really consider focusing more on "Customer Obsession".

In the short term maybe, in the long term, having achievements, voice chat, friends and invites may be good. I personally don't play games on Epic because I like having achievements and stats tracking for example. I'm not sure what the multiplayer experience on Luna is, can you invite people to play coop games? Voice chat with them?

Voice chat is unnecessary to me and many folks, we use Discord or Skype.

Local co-op is a thing in Luna, but I'm not sure about online multiplayer. But in GeForce Now I just used Steam and it worked flawlessly.

Stadia supports the UBISoft+ channel just as Luna does. It's in beta now.