Ventajas
Strong solid company that is stable for the most part. As long as the government is somewhat stable. There are a lot of intelligent people that work there and the work life balance is very manageable at the Individual Contributor level. If you want a good stable job with good experience this is a great environment.
Desventajas
Typical Cons of a Government Contractor. Culture is very slow moving and you sometimes have to work with unmotivated employees. The annual increases are relatively low and you have to fight for any increases outside the normal cycle. Promotions are typically based on years of experience instead of performance unless you make a good relationship with a manager that has power. Management is very political and this gets in the way of the teams trying to do work.