Pros
Good job security, good vacation benefits (3 weeks per person), generally friendly people to work with.
Cons
You're treated like a cog in a machine. You stay in whatever job your management decides to place you in until the contract funding runs dry, then you get placed in something else you'll like even less. Management says they care about your career development, but then they don't approve any training (provided any training exists, which at Lockheed Martin, that's a big question). The motto for career development is "Manage your own career," but they don't give you any power or authority to look for other positions in the company and they don't pay much toward college tuition. Pay and benefits are substandard compared to the rest of the industry. I went to Northrop Grumman and got a 15% pay raise for jumping over, and I got the same insurance benefits for half the cost. The 401k benefits were almost identical, too. The pension plan at Lockheed Martin went away in lieu of a capital accumulation plan (CAP) soon after I joined which changed the vesting from 5 years (pension) to 3 years (CAP). Basically, new employees got vested before I did, and I joined the company a year before they did. The vacation benefit is a hoax because you never have enough money to take a vacation anywhere; they seriously don't expect you to take vacation, either, as they have a cap of something like 500 hours of accumulated vacation.