Pros
One of the best things about Microsoft is that you are working with smart, motivated people all the time. You will find great challenges and be inspired by your peers on a daily basis. I'm always growing and learning. This can be untrue in certain teams, but in general I've found this to be true for most of the teams I've worked with. Loads of opportunity to try new things. I've worked on many different products and gained experience in multiple roles. You can truly change your career while staying in the comfort of the same company.
Cons
Politics becomes a part of your everyday pretty quickly as you move up in the company. There is a lot of overhead to get sign off on changes and move forward with something new. They want to be agile, but this is the biggest obstacle in actually being good at it. There is a lot of pressure for moving up. This is a good thing in a lot of respects, but can be stressful if you find yourself on a competitive team where moving up is difficult, or if you want to coast for a while career wise and focus on other aspects of life. It's not the place you can just do good work and not worry about promotions. If you're not moving up, you are eventually moving out.