Pros
Microsoft has a ton of smart people who are generally really nice to work with and by and large highly motivated to do a good job and deliver consumer value. The review process is generally pretty fair, with good work being recognized and rewarded. The company has great benefits and treats it's employees well. The large size of the company gives employees the ability to pursue opportunities on a variety of projects without the hassle of changing employeers.
Cons
Microsoft leadership has been in a downward slide for the last 5 or so years. The amount of politics involved in decision making gets more extreme every year. It can be incredibly frustrating to be part of a company with so many resources but that is so hamstrung by it's upper/mid-level management that it can't effectively act.