Upgraded my iPad yesterday. Other than insisting it couldn't log me into iCloud, when it turned out it had, it went smoothly. Encouraged by that I did my iPhone this morning.
The phone went not quite as smoothly. First it pulled the same "can't log you into iCloud" stunt, then twirled endlessly on fetching the new end-user agreement for it. Having read the best cure for those problems is log out of iCloud, reboot the phone, log back in: That's what I did.
During that process it claimed to have sent me a verification code it had not, in fact sent. I told it I hadn't received it and send me another via text message, at which point it simply logged me in! One or another of the codes later showed up on my iPad. Never did show up on the phone. Seems like their process is a bit b0rk3d in this respect.
Watch upgrade was slow, but uneventful.
Later, when I tried to make a call, I found I had no service. Rebooted the phone again and had three bars. Hmmm...
The upgrade process hammered the phone's battery. By the time all that was done it was down from 100% to 54%, so it's back on the charger. The new battery health thing claims I'm GTG with 85% battery life. The upgrade didn't much affect the iPad's battery.