Pros
GSA has some very interesting offerings (Fleet, Buildings & contract managements) which allows for opportunities across the agency. It is relatively easy to move around the agency into different positions if you feel the need to try something new. Location, Location, Location - Close to the White House. Living in and around DC can be great (once you figure out traffic), the culture and opportunities that are at your fingertips are fantastic.
Cons
Bureaucracy will eat your soul! This was my first job out of college and although I had some great experiences and opportunities the constant struggle of bureaucracy will eventually kill your spirit. Cost of Living in DC area is ridiculous for entry level employees, you are either living an hour out of the city or you are truly living paycheck to paycheck (all the while eating Ramen).