Pros
Benefits: 4% matching 401k. full health, vision, and dental benefits, including short and long term disability. decent salaries. $250-$500/yr for job related materials. They can carry a lot of agency clearances. As long as you are on a contract, you will have no issues staying employed.
Cons
There are 150 people in the DC area (several hundred more in random other places - like Dayton). Most people are on-site, so they have no interaction with each other. My boss lives in New Mexico and his boss lives in Arizona - just to give you an idea. Also, I've had very few conversations with any of them. They don't have any form of transparency. They decided to move people to a different building and neglected to tell anyone that was moving. However, all of the management was aware. Also, if the company loses the contract for any reason, you are out of luck, as they have nowhere to park overhead staff. They will let you go. And they've been losing contracts like crazy. Also, though they suggest a training/school/conference budget, you will never get it approved.