Random assorted thoughts as someone who worked at Google at the time of launch (but not on Stadia), and now works in the game industry proper:
Props to the engineers, the technical base was there. It really just worked. You could load a AAA game on a Chromecast, and play it. Unfortunately, it didn't work perfectly: From some users it didn't work at all (bad when this was someone reviewing the platform), and for serious gamers the input lag was noticeable on games where it mattered.

Others here are saying Stadia should've been the Netflix of gaming. Here's the thing though: Netflix isn't even the Netflix of Netflix anymore. The streaming industry is now split between the large content producers each having their own platform. Netflix survived this only by becoming a content producer themselves. Smart people at the major video game publishers have seen this trend, and to the extent streaming is going to be a thing, want to skip to running the platform themselves.

The launch was a mess. They said it'd be available at a certain time, but that's when they started a slow roll out. This didn't meet gamer's expectations, where good launches just turn on a game. The lesson here is that if an engineering process (eg, Google's usual practice of slowly rolling it out to make sure it doesn't fall over right away) is going to drive the user experience, clearly communicate that.

The suite of launch games appeared to check the boxes of a good launch lineup, but didn't actually. They had major AAA games on launch.... that were all out elsewhere for awhile. They had big games launching on the platform early on....except actually they were delayed leaving a drought of content. They had a good number of games to carry them through the first year... but no "platform sellers" which would on their own get users to try out the platform.

The target audience was misdirected. It feels like they tried to get the core gamer crowd, which are those who would be the harshest critics and have the least benefit (they have their own systems already).

Their commercials were a bit much, and failed to explain what the platform actually was: https://www.youtube.com/watch?v=A6Wy_pWscsk

The landing page, on boarding process, and value proposition where an absolute mess. You could outright buy a game and play it, but they didn't really tell you that. They had a Netflix like subscription where you got games, but it was a weird system where games would rotate onto the subscription but you could keep them as long as you were subscribed. The on boarding process also immediately tried to get you to sign up to the trial for this service, which fed the impression that this service was required. The subscription also increased the resolution of the games you were playing, but only sometimes and there was no way to know what resolution games were actually being rendered at.

Phil Harrison has now overseen the launch of the Playstation 3, Xbox One, and Stadia. He should be unemployable as an executive, and be weary of anyone who does employ him.

Stadia hilariously lacked a search feature for nearly 2 years. From Google, you know, the search company.

From my time at Google, I saw many people who understood the business of video games. Lots of great insight there. However, I only saw one person (there were likely others I didn't interact with) who understood video games themselves, as a form of art and entertainment. They were on that development team that Google canned, as the first sign that Google was giving up on Stadia.