Pros
The projects and clients you get to work on are world class. Many opportunities to prove yourself and prove to yourself that you are capable of great work and contributing to great work. The work is the biggest reward.
Cons
The work is the biggest reward. Everyone works so hard and at such a hurried pace that it's quite common for your efforts to go unnoticed. There are not many opportunities for advancement, I think especially if you're a woman. There is very much an "old boy network" mentality in place that cannot see past their favorites. The culture and people can be diverse and exciting but with that comes cheap, untrained, inexperienced staff. This formula can bring fresh ideas, cheap payroll, and the same mistakes and missteps year after year.