There's a great feeling that people won't bother you if you do your work well. The executives always think of the employees which builds a strong sense of job security. The insurance benefits here are great, there are mobile career opportunities, and good creature comforts.
They also spend a decent amount of money on employee growth and learning.

Working within Microsoft as a vendor this year helped me see why their software is so poorly designed and riddled with bugs. I immediately sensed and witnessed a culture that drives poor decisions and processes. For example, here I was, working on a VERY complex project, for a company that has a product called, "Microsoft Project," and they weren't even using this program! It was surreal. They had NO UNDERSTANDING of the project activities or the relationships between those activities; and they were clueless while also maintaining the arrogance that is the blood that flows through the arteries of the culture. I could write a book on how bad this company is at executing a project. But, more importantly, this demonstrates how a ruthless monopoly and unfair competition can drive extremely poor products in a key area of American business. I would NOT buy Microsoft stock. Their culture is not curable and much of their dominance is clearly doomed.

Everyone knows another layoff is coming, and they don't want to be the low-performing guy on the team, so there is no job security. The job can be very tiring and demanding due to the large amount of work and deadlines.
The big negative thing about working at a place like Microsoft is definitely that it is a really big company.