Pros
I have colleagues I deeply respect and really like as people. I enjoy being at the office and I'm not (so) sad when it's Monday morning. But it is a huge organization so it depends on your department. Also the benefits, as others have noted, as are good as it gets in our industry and better than many of our competitors. And I enjoy working in Dupont Circle.
Cons
With a new CEO, we may have some hope for a positive emergence from the mess of the merger, after which morale dropped like a rock. Waffling on decisions about restructuring the company has led to confusion. The movement toward field office-centered program management is probably a wise move, but it does mean fewer positions at HQ in Washington, and there is no sugarcoating that.