Pros
You are able to gain leadership experience managing teams, working with large budgets, and building advanced technology products very quickly: a true meritocracy. Self-starters who are able to get their own funding through government agencies and customer contracts get to have the experience of running their own small (and in some cases large) business. Lots of research and development opportunities where one can be surrounded by PhDs and the best RF and Radar engineers in the world are usually plentiful. Publishing is available, bonuses are given for outstanding work, bonuses given for each patent filed. Engineers here that move up will be some of the most well-compensated across any field. The executive and management population is aging rapidly and quickly retiring, creating great opportunities for advancement in the next several years.
Cons
As with any big company there is bureaucracy that slows down innovation at times. There sometimes seem to be endless processes. If you are unable to obtain high level clearances, your career success will be limited. A lot of the really interesting work is classified and cannot be published or even spoken about to uncleared people. You usually obtain projects to work on through your contacts and people network within he company; this can become politicized and is rough on newer employees. Defense industry funding is highly subject to the whims of congress. No stock options or large bonuses are given until an employee becomes relatively highly ranked, at the executive level.