Pros
American Express really cares about people, both employees and clients. Amex about doing the right thing. It is a serious company that walks slowly because it walks firmly. People are good and it really is a great place to work.
Cons
It is a bank. No matter how cool the new tech behind the screen looks, banks move very slow for safety concerns. Although those concerns are very well founded, the paranoia makes for work to be extremely focused on security and development is hard since there are so many security features. Also the work can sometimes become somewhat boring for creative minds and vertical mobility is very slow. However, depending on our career priorities in a specific moment of your life, I really do believe that the Pros far outpace the Cons.