I got it earlier today on my AT&T Note 5. Lots of user interface changes/tweaks, some new battery management/phone optimization stuff, I'll have to play with it some more to see what else is new. The upgrade went smoothly with zero problems.
Had it on my 6P within hours of it first hitting the stream in the summer. I enroll/un-enroll in the Android beta program at will when new releases are about to come out so I don't have to wait. Just got the 7.1.2 update last week. I use Nova Launcher and have it highly customized, so whatever UI changes there are I typically don't see them. Two of my of my favorite improvements, albeit two very small ones, the ability to switch between open apps by double tapping the Overview button and the Clear All function on the Overview screen.
I tired that a few times, and couldn't get it to work.
Not a big deal for me. The last time I used a front facing camera was back in 2010 when I had my original Evo and used Fring with a buddy of mine who also had an Evo. No other phones had front facing cameras at that time, Other then by accident, I don't think I ever accessed the front camera on the Nexus 6P, and I certainly never took a picture with it.