Pros
Wide range of highly diverse and open-ended technical work. You can learn a lot in a short time and get a lot of control over your own parts of projects. Good work-life balance and very hands-off management, allowing staff to control their own schedules and telework as needed. Excellent day-to-day work atmosphere with very accomplished and friendly colleagues. Great 401k and vacation benefits even after recent cutbacks, nice campus-like offices at main sites, and little bureaucracy or onerous rules compared to other defense companies.
Cons
Technical people have zero career path and disproportionately low salaries. Promotions go to consultants and bureaucrats with government connections, with even high impact technical or research work not rewarded. Lots of older staff entrenched in the higher positions, and openings are usually filled by new hires instead of promotions. Not much research going on except in one or two departments, and the internal research program is increasingly useless and all about business development. Unlike other FFRDCs, they place little value on having a PhD or your own research agenda, so PhDs get a raw deal and are often under-hired. Many projects are initially fascinating but ultimately fall through, and the main thrust of the company's work today ("systems engineering") just amounts to IT and management consulting.