I have to say that the whole system is pretty impressive... it sounds like they're effectively creating a new internet for their games through their data centers. At the moment my internet is hugely iffy... but I realise I'm probably an outlier in that regard in my area.
My worry is that games may no longer be for purchase. I'm sure we've all had situations where we're watching a show and it disappears from our streaming service... or a show we're loving is no longer available because the company that pays for it is creating it's own online streaming service (CW or DC as an example)... I imagine this will be all the more frustrating for games. I currently have a PS4, but can't play with my friends on XBox. Stadia solves the hardware issue, but just replaces it with a subscription issue... I'm on Google, but my friends are on Apple or Microsoft or NVidia or Value or Amazon... and I'm sure each platform will do it's best to lock in the best developers/publishers.
I think more competition in the area is good, but I'm worried that overall the customers will lose out, as we go from PS4/XBone/PC and splinter off into more and more monthly subscriptions. Should be interesting to see how it all plays out.