From my point of view, the things I've most "noticed" coming from MS that are great seem to all have been launched/started during Ballmer's days (2000-2014). For me those are:

Office/Word Online (2010)

Azure (2008/2010)

WSL (Can't find info. Looks like it started before 2014 under Project Astoria)

.Net Core (Happened in 2014 - not sure who "started it")