Vantaggi
Microsoft has the best health benefits on the planet. In the 10+ years I was a blue badge, I think I only saw 1 medical bill that wasn't 100% covered by Microsoft's plan. In fact, Microsoft probably has the best benefits package in the industry outside of Google (comprehensive medical / dental / vision / prescription drug plans, paternity & maternity leave, 5 weeks of vacation / year after 12+ years of service, company store, company library, Prime card, Pro Club / gym membership, Connector bus / metro pass, free beverages, and many other benefits). Also, despite it's size, Microsoft is a fairly agile company. The decisions that senior management makes usually are rational. And there are very few companies that as much state of the art technology as Microsoft does.
Svantaggi
Unfortunately, Microsoft is a really big company and the corporate bureaucracy is most acutely felt during review time. Review goals are often made irrelevant by changing requirements during the course of the year and the review process is lumbering and is often times burdensome. Your career advancement & opportunities are often determined more the by subjective opinions of ill informed managers, than by merit & objective facts. If you have a good relationship w/ a good manager, you'll probably go far in your career. If you have mediocre manager or one that you have a strained relationship with, you should switch groups or leave the company, ASAP. It's easier to advance your career outside of Microsoft than inside of it. The stock based compensation (options, grants & ESPP) isn't anywhere near what it was during the 1990s and the base salary hasn't made up the difference.