Vantaggi
Great entry level opportunities, good starter (company) name for a resume. Depends on the dev group, but the tools and testing are better than most other software companies - you won't be able to take all the methodologies away to a start-up... People definitely return your professional phone calls - "Microsoft" still has "pull" in the general business community. Great benefits, though the benefits aren't terribly better than others - Microsoft has a $0 co-Pay, whereas, at least to me, a $5 co-pay is functionally the same. Microsoft has some of the biggest brands in the industry: nice to say "...I improved calculation speed in Excel by 175%..." if you get the opportunity to work on a big product. Many of the the people are first class, really decent.
Svantaggi
Intensely political; managers are distracted from the essential work of managing by political considerations, "Managing upward" is the key to career success - lot's of attitude without credible results. Bad decisions are made regularly because short-term thinking dominates. A very strongly hierarchical culture - that is too big for hierarchies to be effective. Lot's of teams going nowhere: not cut, not funded for success - career deadzones. Deadening series of meetings: coordination is necessary, but heaven forbid there a technology to cut away the endless meetings that sap productivity. Poisonous managers, as probably has to be expected in a culture that has so many, but offers no training, except for how to avoid lawsuits.