Got mine today.
Viewfinder is bright and clear albeit different to optical... so nice having histogram in there though and actually seeing the exposure. That is amazing.
And little things like on start up it will tell you if your lens is in manual mode and you get wavy red lines if the manual focus peaking is on, or you can magnify the selected AF live in the viewfinder. Or there's my current favorite - the blinking GPS indicator to tell me that I need to run the Canon Connect app on my phone so the camera can embed GPS info. (Beats putting on the GP-E2 which I often found had a dead battery because I didn't turn it off.) The info load is amazing and useful. Be sure to turn on the feature to rotate the info in the viewfinder when you rotate the camera to portrait orientation. Breathtaking
For a first gen mirrorless ... well done Canon this line is going to be even more incredible once the wrinkles ironed out
Mostly, I think the wrinkles are in our brain, like those pictures of fighter pilots enduring 10 gees of acceleration. I was skeptical at first. I customized the buttons, etc, but backed stuff off other than putting the depth-of-field option on the AF ON button and ISO on the EF adapter ring. I did create two My Menus. The interface is pretty solid once you stop thinking 5D and think EOS R. I had to spend time doing that, but, whoa!
(My EOS R blog: https://eosrreview.wordpress.com/)