I think he made one hideous strategic mistake -- deciding Microsoft was the Windows company instead of the Office (or "whatever makes money") company. If he had reacted to iOS and Android by selling Office for those platforms Microsoft would probably be making money off the mobile revolution instead of facing oblivion (or at least irrelevance). (Recall that Microsoft makes, or used to make, more money per Mac than per Windows PC.) Instead by emphasizing Windows over Office he made a whole bunch of people realize that they don't need Office to get through their days.
Betting on Windows was, I still think, the correct strategic decision.