1) The experience will be inferior compared to offline gaming.
2) One benefit I can see from Stadia is if you haven't played a game before, you are checking out a walkthrough on YouTube, and you want to play it yourself for a couple minutes to decide if you want to buy the game to play offline. After that, I would purchase the game on a traditional console if I liked it.
3) Gaming shouldn't require an internet connection to check if you have the rights to play it. Ever.
I want to comment on point 2 - I don't think these streamed games are going to be free. In fact, I suspect they're going to cost just as much as everywhere else. I don't see any reason why say, Madden costs $60 on Playstation and Xbox online stores, and in Gamestop and in wal-mart etc.... and is suddenly going to be free on Stadia. Perhaps there will some kind of monthly subscription service like EA Access, but it definitely, definitely, wont be free.