Pros
An inspiring mission for those who care about national defense. Depending on the group, can have extremely interesting and value-added work tasks. Excellent benefits and work-life balance. At least for me, excellent and supportive coworkers and great bosses. Ample encouragement to seek additional, company sponsored education. For me personally, I have found a niche that suits my desires and am quite happy with the lab.
Cons
As with many organizations like this, many rules to navigate in order to get work done, especially operations-oriented work. Other groups that you may depend on don't necessarily share your goals. For some (speaking for engineers), work can consist more of project management than actual technical work, which can impact professional personal growth. Additionally, not many opportunities to interact with organizations outside of the Defense Industry, or global organizations. Compensation is about average.