As one who can recollect the old days where one had to pick up the phone and read catalogs to source a supplier, I'd suggest he didn't do that bad - MS is still around and generating billions, after all. But he botched a few potential growth vectors along the way - think mobile or SaaS.

By being unable to use his warchest on a changing market. As an example: missing the smartphone boat twice (once with Windows Mobile vs Symbian, and once with Windows Phone vs iOS/Android). Another example: Microsoft search / Bing.

Microsoft kept Office relevant though, made Azure relevant, and are reinventing themselves from a proprietary to a data company (like Google, Facebook, and Amazon) who also do a lot of open source (like the previously mentioned companies). But I suppose Nadella takes credit for that.

My opinion, fwiw:

Financially, no.

Optically, yes.

(and, in fairness to the latter, in a manner which was diminishing longer term value creation also. However he totally does not deserve the reputation he generally has with developers. Like a lot of things, folks love to view them in black in white, when in reality it's a rainbow).