There are people out there who like to blame this man for Microsoft's ills. Here's the problem with that: everything that's wrong with Microsoft pre-exists Ballmer's leadership and goes all the way back to Bill.
When people sit there and go: "Well, he missed tablets... and phones... and... " well.. they'd like to forget that Microsoft almost never leads markets - which is odd given how much money the company spends on R&D - but instead gets dragged into them once someone notices they risk the core business model. Just look at recent history: The Internet... not important, until someone realized it was... Consoles... not important, until Sony started talking about using them to control the living room and home computing experience then... Hey Sega... oh... that didn't catch... err, quick get that in house... Music Players... wait... Apple's making how much money... tying up industry partners... and people are liking them enough that they're doing what????
Someone could likely do a more complete list, but those are the big ones from the tail end of Bill's reign to remind us that Microsoft's history is largely not one of market leadership, it's of being led by the nose as the tugs get hefty enough to get their attention. Especially outside it's core competency of servicing business needs.
There are reasons for that. Some folks like to blame "protecting Windows" or "protecting Office" but it's more broad than that and you've also got to give that protectionist nature its fair share of credit for actually getting MS moving sometimes. A far bigger problem is having to balance everything against retail partner needs: if Dell and HP aren't asking for Tablet OS's, you're likely not making Tablet OS's unless you're willing to go into the tablet business for yourself. Apple doesn't have that problem, nor Google to the same extent 'cause Google is basically looking where you aren't and aiming right into the market where MS barely had a foothold to begin with. There's also the reality that, despite the mass investment in R&D, there seems to be less time invested in foreseeing mass consumer customer needs and wants; placing the companies that do spend a lot of time on that on far more solid ground within their original launch windows and feeding a lot of "me-too!" initiatives (see: half a dozen incompatible short lived tacks at "killing" or, hell, just trying to "compete" with the iPod). Hence, the long established jibe that MS always catches up... about three product revisions later.
The problem now is that catching up in three isn't good enough because these days, by the time you ship those revisions, you've both built up a reputation of making things that aren't quite good enough/are shit and the market's moved on to the next thing as tech trends are moving an order of magnitude faster than they were in the 80's/90's. The best example of that is Zune where, by all accounts, the software/hardware combo finally got good enough just in time for the entire world to go: "Fuck Media Players, gimme my iPhone/Android that does it all!"... and the paradigm shifts again rendering your "refined" product irrelevant while pointing to the glaring reality that you've got nothing to slot immediately into that which replaced it.
Solving that when the corporate culture of "stay the course until the iceberg is this >< close" is so firmly ingrained amongst the workforce requires more radical transformation than just replacing the CEO. You'd need to weed the place from the top down into management as a whole. That's just not likely to happen because the same shareholders that are calling for Balmer's head aren't likely to tolerate project delays or too many bad quarters while someone puts things "back into order". People like to look at Apple and go: "Look at how Steve Jobs leads that company!"... but they gloss over the reality that Steve's built a pretty solid team of people under him and "groomed" them over years in his ideas of design and product focus until they are able to bring him things that are already 90%+ baked to be tweaked to precision; that's just as important.
The alternative is to do what the DoJ tried to force them to do after Netscape and break the company up so that it's divisions can better focus on their core markets without being bound by rules of engagement that prevent them from risking any other product. That's not happening either.
Maybe we just have to accept that MS's place in the industry is to be its 500 car steam train with an old cranky radio: it's a bit slow to get messages off the telegraph, and takes a while to stop and change direction, but it's going to build a great deal of momentum once it gets going the right way again. Replacing the engineer won't change much of that reality unless you're prepared to live with the necessity to shed some cars and/or cargo to reduce mass too. But, if we're going to make that acceptance then the bigger question becomes how long you're going to let successive engineers run the train as is lest they eventually learn of a paradigm shift too late to stop it from going off into the gorge...