I woke this Sunday to find that my Apple Watch stuck at the Apple logo. I tried the recommended fixes, hard reset (no change), power down (could not get power-off control), etc., all to no avail.
Finally, I started a chat with Rachel at Apple. She was very helpful and we discussed the situation. We concluded that it was time to send the watch in for recovery. Since it's the holiday season, I chose a mailer rather than brave the mall near my home to get to the Apple store.
To prepare the watch for the return, Rachel asked me to go to my iPhone and un-pair the watch. When that completed, the watch switched from the logo to the pairing screen! Life!
When I re-paired the iPhone and the watch, the watch updated, paired, and all is well.
So if your watch gets stuck at the logo during an upgrade, here's another step to try: un-pair it from your phone.