Pros
The diverse set of talent across the organization, helps to keep you exposed to new ideas and forces you to understand your own career inspirations/direction as many folks just know what they want to do when they 'grow up'. Pay is reasonable and if you are in marketing this is a premier brand to take with you anywhere.
Cons
In a word, bureaucracy. Amex is the premier expert in creating silos and tearing down ease of work in order to increase the complexity of doing business. Many times the ideas are sound and might even make sense, until you've been around a while and its clear that politics are usually the biggest drivers for centralizing or decentralizing (and back again) a specific organization. The fact that we are in a very challenging time almost allows this type of behavior to go on, the best power players will survive, those with less skill will be posting on LinkedIn...