Pros
Huge company with plenty of room to grow & move. With so many offices worldwide, you are able to really work where you'd like, if your position & experience allows it. Currently am working on going to Africa for a month with a former school group and working with Marsh to work remotely and with the African offices.
Kontras
Very political, as you would expect from a company of this size. The tasks of a Client Rep are very boring, as you are basically half a step above an intern. It helps to learn the business, but be prepared for monotonous task. Also, a very rigid company. They call themselves the "Harvard of Insurance," and their track record stands behind it. That also means you get that stiff, sometimes stuck-up attitude from people.