I was updating the Watch to OS2 and after 4 hours, the watch rebooted and shows an exclamation point, and says www.apple.com/help/watch. It was never removed from power, and kept it until it rebooted.
Apple Watch 42mm, iOS 9, Apple Watch OS Update
Click: Apple - Support
It will redirect to this page: If your Apple Watch displays a red exclamation point - Apple Support
... which will tell you to do the following:
Force restart your Apple Watch: Press and hold both the side button and Digital Crown for at least 10 seconds, until you see the Apple logo.
If force restarting your Apple Watch doesn't resolve the issue, contact Apple for service.
Update failed! Now Watch says Exclamation Point and www.apple.com/help/watch! What to do now?
