Pros
Steady work (usually), flexibility to move between projects, great early career and late career resources. Better pay than traditional government work, better work-life balance than traditional consulting - easy to keep to 40 hours a week if you manage your time. There used to be a great internal R&D program, and that might come back.
Cons
Technical career path non-existent, despite efforts every few years. Shopping for a new project is basically a mini job search where you get laid off if you spend too long on the bench. Finding new project opportunities and career advancement is entirely down to networking and office politics. There's high variance between departments and projects, it's easy to get stuck on a bad project, and not always a place where hard work pays off.