This dependents on the organization, but for me the flex time, collaboration, project opportunity, and benefits were all fantastic. Also, with the 2014 HR changes, it is much easier to manage your career across the entire company. If you've got the talent, you can go where you like.
Cons
Microsoft is a large corporation with share holders. Sometimes, decisions are driven by that and not by purely technical or consumer driven possibilities. This sometimes finds its way into corporate and organizational culture, and at times feels a bit poisonous.