Avantages
Generally, most of the software system programs tend to be command and control oriented with very little web technology related work. Most of my peers were generally very competent with some being extremely sharp and creative. On low intensity programs, the low-level managers were usually very supportive of a balance between work and life. For me, most of my experience has been in using core language features of Java and c++ in application servers. Corporate leadership appears genuinely concerned for the employee quality of life and work and tries to seek a good balance between it and meeting the customer's needs. The company benefits are very good as far as medical, dental, vision, disability, life insurance, and 401k.
Inconvénients
Depending on your background, you could be pigeoned-holed into one type of position, with very little chance of cross functional opportunities, as in going from software test engineer to software engineer and vice versa. Since the company is heavily dependent on defense spending, there is usually a strong correlation between cuts in defense spending and a lack of jobs. On high intensity programs where the delivery schedule is tight, expect to work alot of overtime. Business level and program level management tends to be more focused on meeting bookings and profits with very little time spent interacting with the employees.