I've only played a couple hours on Stadia ,but so far its been really good.
I did turn on Visual mode as performance mode looked like the PS4 version, then turned off Lens flare and chromatic Aberration to make it look clearer.
Also found the controls to be odd as it had Aim acceleration on, eventually found out how to turn it off and it feels so much better, i can aim more precise now whereas i was going past targets due to the speed increase of the acceleration.
The only issues i've face have been ladder issues at the start, i could climb it but not get to the top, after saving, quitting and loading in again it worked, the other was more a graphical glitch of a dude sitting down in mid air, when i drove past he was gone and crossing the road.
The Audio on this is superb though, have to put headphones on and cranked up.