Chromecast - better than all the alternatives but they could have gone that extra distance to make a whole Google TV apparatus and didn't.
Pixel phones - when they had all the critical mass they fumbled and released an entire line of very mediocre hardware
Pixel laptop - one of the best laptops made, ever, but they didn't commit and it was a one-off...
Hangouts - could have been the messaging app for everything... Instead they split it into two and now FB Messenger is the messaging app everyone uses (outside the US anyway).
GCP - again, they had a chance to become what Azure is or bigger but just seemed rather uncommitted to it...
Stadia - if they had committed it could have been huge because it absolutely does work very well. The concept of it working with Chromecast was good so again, they could have again, just made the TV box, bundle a controller and it's a console for everything... But nope, cancelled right as gaming Chromebooks are coming onto the market...
It sucks because many Google products are absolutely best in class but there's this eerie feeling that even those could disappear. Google probably has the best engineering in the world but also probably the worst product managers and business people in the world it seems...