Download and install ran smoothly, but my watch has now rebooted to a red exclamation point icon with a link to an Apple support page. I've tried restarting the watch by holding down the crown/button several times but my watch seems to be unable to boot past the exclamation point. What can I do?
Sorry to hear you're running into issues. Per the watchOS beta Software Installation Guide:
"In the event your device restarts into recovery, please visit support.apple.com for assistance."
They should be able to assist you further. Thanks!