Ballmer was CEO for windows 7 (perhaps the best windows ever), heavily expanded MS enterprise and cloud and pushed (against Gates) for the creation of an in-house hardware team. Everything MS is succeeding at today is the result of his tenure as CEO.

He had his share of bad/terrible calls (Vista, killing IE, one UI everywhere, missing the smartphone market window, etc) but overall, he wasn't just a lame duck riding on the success of Gates.