Pros
It has an average salary and benefits package for employees. Generally most projects here will not be too stressful for the worker.
Cons
Projects could suddenly lose funding and they will have to switch you to another project. Some projects are very slow and you won't gain any useful skills. For example, the last project I was on was very slow, there was no design work, and no guidance or direction from any of the higher ups, although the higher ups need not be from this company. But generally all projects are slow to some extent and this is probably typical for a defense contractor. Also there is much politics going on.