I am counting my blessings after reading this thread.
My download was relatively quick ( about 90 minutes) from start to finish.
The only 2 issues I have found so far:
1. my inability to get regular Chrome to load. I switched to Chrome Canary and it works fine.
2. it appears to drain the battery on my Samsung Ativa much faster then 8.1 did.
I do have another laptop to upgrade...but I am giving it a few weeks to see how it plays out with this one.