Pros
As a software engineer your worst fear is getting stuck with a job that forces you to work long hours for little compensation. In my time at Lockheed they have never overworked me and often if long hours are necessary overtime will usually be approved. They offer to pay for your masters, and the benefits are in general pretty good.
Cons
It is a bureaucracy which can be frustrating. Sometimes things are a little too close to a Dilbert cartoon. Some projects can be incredibly process heavy, but it varies widely from project to project. Projects often get cut before completion, which can be disheartening and makes getting motivated for the next project difficult. Also the industry in general can sometimes be incredibly incompetent. Often the customer/contractors want to develop their own proprietary technologies that are often huge boondoggles that work no where near as well as off the shelf technologies. Even when they do use off the shelf technologies, they frequently want to wrap these in their own proprietary technologies, frequently making the underlying technologies more difficult to use with less capability and more bugs. Being forced to use those proprietary technologies is very, very frustrating.