Pros
Microsoft has some really talented people -- sure, they may not have been winning the recruiting battles in more recent times but they've got some deep benches. When I first got there, I was surprised at how many employees there just seem to stay for A LONG TIME. I knew several folks who had been there 10, 13, more years. This was unheard of in the Silicon Valley tech companies where I had worked. I worked hard there and believe that my work was adequately recognized and appreciated. They treat their employees really well. It was pretty hard for me to leave in spite of having a number of solid reasons for doing so. Why? I got so comfortable. It's true. It's a nice lifestyle. Didn't have to work THAT hard. (Not relative to how hard I was working.)
Cons
I sometimes felt frustrated because I was used to doing things to an A+++ standard and so found myself there often frustrated by more Lowest Common Denominator or C-level solutions. That was probably for me the hardest part about being there. It wasn't a cultural fit for me where I love efficiency, nimble-ness, best-idea-wins, and somewhat direct communication style.