Pros
Good pay and benefits and there some genuinely nice, hard-working incredibly smart people who work there. When I first started to work there over a decade ago it was the most inspiring, supportive place to be. I gained amazing communications skills from even more amazing people and grew so much professionally and personally. Those people have all left.
Cons
The agency has become a dead end. They are not considered innovative in the market and have not secured a new, major client since landing Microsoft in the 80s. I have learned so much more about the changing field of communications since leaving. If you don't fit the mold, you may lose your soul trying. I've seen the term "mean girl" used to describe the work environment, and I would have to agree. Senior management is made up of what they call "lifers." Those who have been there 15+ years and who have completely lost touch. The mold to get to senior management is the sorority, alpha female type who bullies and undermines the confidence of those around them to give the appearance of "managing." Senior leadership postures and positions well, but in the end accomplishes fairly worn-out, mediocre work. This seems to be rewarded for some reason. You really don't realize how much confidence you have lost and how much of yourself you have given up trying to move up until you leave, and then you feel as though you escaped an abusive relationship. I know this could be said of many work environments, but I wouldn't chose this again.