Same here. It downloaded seamlessly and I was about to praise Apple for the non-issue of downloading right away. Usually the servers are hung up. I'm at work without access to iTunes and after updating OTA, my 6s is a brick. Cool.
It's happening for some users... if you have backups and iTunes available you'll be able to recover and restore and update... will just take some time.
UPDATE: After first brick error, I restored back to 9.3.5 and tried to download and install again....... SUCCESS! Hope you guys have the same luck after retry.