People blame Steve Ballmer but I think he did great stuff. He built the huge enterprise salesforce and got Microsoft a leg in the enterprise, where margins are much higher and consumers much less fickle. He also chose a very good successor and removed all the old timers who would have made trouble for Nadella (Muglia, Sinofsky to name a few). Microsoft went from mostly an OS+ consumer software company to this enterprise gorilla which will now have an IBMesque lifetime (meaning will survive for very very long) regardless of whether their projects are very good or not.
Sure he couldn't beat the iPhone, but the iPhone is the most successful consumer electronics product of all time.