Pros
There seems to be a breath of fresh air in Microsoft that makes working here both refreshing and challenging depends on what you are looking for. If you are the creative types that like to leverage people's idea to be successful and believe the success of the group equals the success of individual no matter what it takes, you will now find MS a place that actually measure your performance in similar ways. Also If you are the experimental kind that thinks that good business in tech needs to move fast with ideas, you will also find that MS is now a place that wants you to help it move in that direction (surprisingly enough)
Cons
The flip side of the coin I guess is that you are now needing to learn new ways (ironically ... that's actually how the rest of the industries have been doing things for a while) that is different from the Microsoft that most people use to know. If you are just looking for a nine to five job, you may find you have less and less room to go in Microsoft - there are still places for that, but far less common IMO.