Avantages
Some of the work will be interesting. Being a defense contractor, Lockheed Martin is involved in the high tech industry, including the development of hardware and software, that is in constant daily use by many of the largest government agencies sporting three letter acronyms. Contractor work on this level doesn't have quite the safety and job stability as outright government work, but it has more than you would find at a traditional civilian company. If you are technically inclined, and very detail oriented with a preference for hierarchical structures, defense contractors can be a good place to work, and many employees work for ten or more years before retiring or moving on.
Inconvénients
The politics and the paperwork grind down many people. Most of the people have a military background, and so accept the environment to some extent, but there is also a wide recognition that the procedure oriented nature of the company and the back room politics compromise the central mission.