Vantaggi
Microsoft used to be a great place to work and still carries some of the vestiges of that greatness, however since the late '90s it's been on a downhill track. The pay is reasonable and there are great groups to work in. For the most part the people are really what makes the company a decent place to work. The benefits are some of the best you'll find anywhere.
Svantaggi
Microsoft, like all large corporations, is becoming bloated with a middle management that is far more interested in carving out fiefdoms than doing anything either really productive or in the interest of customers. And like all big public corporations, Microsoft is far more focused on the short-term bottom line than the long-term health of the company. The culture is rapidly moving from an open, innovative, and creative one to a highly politicized, disfuntional one. I would rate three of my last five managers as incompetent and totally incapable of managing people. I literally sat through a meeting listening to one manager spout what can only be described as a "Dilbert Mission Statement" stringing together big words into a completely incoherent jumble. I had more than a few managers who could not tell us what success in our positions would look like, nor could they define what our group was supposed to be accomplishing (the worst two of these have moved up in the company). I worked in an organization that had teams of people who could not define what their contribution was, nor could anyone else in the group. When I started at the company there was a clear open door policy and everyone was encouraged to communicate up the change as appropriate. By the time I left many organizations had established a clear "chain of command" and although the the official policy was still open door it was clear that you didn't go over your immediate managers head. Worst of all, Microsoft as devolved from a real customer-focused company to lumbering giant with little or no regard for the real source of its wealth. If you strive for real accomplishment you can still find it at Microsoft but you may just as likely not find it. If you have a real affinity for doing right by the customer you might find it a very frustrating place to work.