Pros
Big company, lots of job openings and easy to move around to other programs or locations if your manager is well connected (which mine was). For the most part, I always enjoyed the work I was doing, and my specific manager was great for career planning. Even though I'm not part of the company anymore, he is still my mentor and we talk regularly. Good 401k benefits, not sure that's still true for brand new employees.
Cons
I worked in a team environment, with Lockheed as the prime and Boeing and others as subs. Lockheed's compensation was average for the industry, but lower than its partners. It can be easy to get lost in a big corporation, and can be very frustrating when you don't get to share in the success of the company (no annual bonus based on company performance). They're very stingy when it comes to happy hours, christmas parties, general employee social events, but that's also not necessarily how you judge a good company.