Pros
The mid-level management and grunt workers are friendly, fun people. The hours aren't terrible by any means, and the pay is very good for the amount of work you put in. I was lucky to meet a few talented people that I will stay connected with throughout my career. The size of the agency was another plus if you enjoy working in small to medium-sized teams.
Overall, not a horrible place to start your career, but certainly not a place to make it.
Cons
Boring:
There's only one real client and the upper management team WILL NOT step out to explore new ways of advertising for them. I'm not talking about fancy new technology or whacky "out there" ideas -- just fresh thoughts and a new approach. They're perfectly happy to do the job of any in-house team and simply toe the line of same-old, same-old.
Cliquey:
The creative leads have their favorites and they are not afraid to show it. It can get very uncomfortable when you enter a room and get the feeling that your partner and their pet-creative have been talking about you. If you're not in their clique, they will let you know.
Stagnant:
One major client is more than enough in their eyes. During my time there, I saw no effort to bring in new clients, expand business, or secure the futur of the firm should that client decide to go into review and leave for another agency.