Pros
Benefits (pay, insurance, flexiplace, flexihours), stability (they're really never going away), challenge (tight deadlines, high visibility, complex work), importance of work (lives aren't on the line, but funding our country matters), variety of work (easy to get re-assignments within the organization to do different types of work), advancement opportunities (this is dependent on the President and Congress budget, but I've went from a GS-2 to a GS-15 over the years). They do look after their own.
Cons
It is a bureaucracy and things move and change slow. Though it moves faster than most agencies due to being in the public eye so much. Being in the public eye can also be a negative - knee jerk reactions from the media/public/congress can impact your work. Executives react poorly to that sort of pressure and deadlines will be shortened regardless of the impact. The negative stigma of working here can sometimes be troubling.