Vantaggi
Compartmentalized security clearance makes you more marketable in defense industry. If you are software engineer, programmer, computer science major, mathematician, physicist, you'll be well sought after at this site.
Svantaggi
No growth path for technical oriented people. Slow promotion. A big problem is that you see fairly common people with 15-20 years of experience doing good work continue to be E3 where in other defense companies they would be E4 already. Serious communication problem at the senior management level. Senior management lacks trust in their senior technical folks. Decisions are managed via a strict chain of command hierarchy. Among management level, it seems status is everything (ie. who has the biggest office).