Pros
When starting a career out of college, it's hard to beat what's offered at Social Security. After a year, I was making over $50k, which in Kansas City, was quite a bit for a 23 year old. I had optional overtime, which pushed my salary to nearly $60k. I had great benefits, smart coworkers, and it greatly expanded my knowledge set, which allows me to pursue other jobs outside the agency.
Cons
Promotion can be difficult. The hiring process is quiz based, to protect workers from favoritism, but in reality is promotes lying on applications. Not knowing that I HAD to lie, it's been years since I've been promoted, despite having stellar performance reviews and details that most others in my position have not had. Work can be tedious, and part of my job was on the phones, which were a brutal part of the job. The work can also be subject to budget and congress. Overtime may disappear for years on end if congress cuts funding, bonuses may go away, and a government shutdown means you don't get paid until it ends.