I definitely thought it was an upset but as early as 30 seconds into the fight I could see Rousey was in trouble. I don't want to take anything away from Holm, who fought a perfect fight, but I thought her job was made easier by Rousey's ego. It seems like Rousey liked to beat people at their own game, like when she beat Correria standing up, but it was obvious that Holm is a fair more accomplished striker. At that point, Rousey should've done everything she could to take the fight to the ground.
At the end of the day, Rousey is a world class judoka who has learned to become a decent stand up fighter. She was up against a world class striker who had solid takedown defence. Her best chance was to take the fight to the ground and go for the submission. The fact she didn't seem to try to change her tactics speaks volumes about the quality of her game plan, as well as the poor advice she got between rounds.