Pros
Big company hand-holding. Very good benefits. A number of projects that only big-gun defense contractors can get. Depending on where you are, you can be working with some really good people. Much better for technical work than management.
Cons
Big company bureaucracy and irrational processes, well beyond required for defense contracting. Lots of un-accounted for time, particularly if you are in management, where you are graded on the curve. It is a "40 hour nominal" but really 50, 60 if you are trying to get anywhere, with lots of fuzzy expectations. That fact is not remarkable, but the refusal to keep track of that makes planning a lot harder, and tends to lead to fake plans. Lots of straight communication noise and rules that are irrelevant to day-to-day operations. I feel like I am supporting a lot of heavy weight that is paid to get in my way. Lots of unexciting projects that big-gun defense contractors generate for job security and revenue.