So I upgraded (I'm just too impatient and I had a gap in work).
I did a complete wipe and clean install as I always do with a major update. I've had a few issues over the last few days.
1. I'm running a 15" MBP 2016 hooked up to an LG 5K ultra fine most of the time in clamshell mode. Sometimes I also plug in my LGUD88 (4K) and it is incredibly temperamental and I can normally only get it working by a mixture of swapping the port it's plugged into a few times and restarting.
2. It mostly just hangs and I get the spinning beachball when I try and restart. I have to force a restart and then it actually just shuts down instead. (I'm only restarting because of point 1!) Restarting seems longer than in Sierra.
3. My Drobo 5D keeps switching itself off after a restart. I have to turn it off and on again to get it working. Not great as I use it as my Time Machine.
4. Two mini points: this morning, my wallpaper was missing, just a black screen until I restarted. I've also had the CC app randomly log out.
The good news is that I'm not experience any issues with InDesign, Photoshop or Illustrator. And Office 2016 actually seems to work faster. Nothing is 'terrible' but it's likely my worst upgrade experience.