Oh right, I had forgotten that - as least as spun by Apple PR.
I'd argue that it is hardly a 'completely different operating system' (unlike the big move from the original 'Classic' MacOS to OSX). Its still just an upgrade (even Apple calls it this on its own site -https://www.apple.com/ca/macos/sierra/), albeit one that may prep things for their new Apple File System - across all their OSs - but not out until next year. Changing the name of the OS does not change that.
Mostly, its just another update with the usual crop of bells, whistles and security updates. Nothing Insanely Great or One More Thing. Should'a been in the Updates section of the App Store for applicable Macs.