The biggest dread I have before running nowadays is dealing with the WatchOS 4 music app. Normally it’s just general bugginess, but today there was no music synced to the watch at all. After about ten minutes of trying to sync anything over to the watch, I just gave up and ran without music.
Perhaps the most damning thing I can say about WatchOS 4: not having to deal with that app far outweighed the annoyance of not running with music.