Pros
The company is well-established and respected, so having it on your resume can look good. If you fit in with the team you are on, it can be a good environment, with your managers seeking out positions for you and helping you move ahead.
Cons
The company has become even more hierarchical and autocratic than it was when I joined 8 years ago. It has changed significantly from when it was a private firm. In addition, the government client is no longer the easy "cash cow" it was traditionally. It is trying to maintain the image of itself being a thought-leader, but generally we have become a "seat in chair" operation -- contractors rather than consultants. New grads and inexperienced employees make the company more profitable. Some teams feel like "sororities" rather than a professional team.