Pros
American Express prides itself as a company that values work/life balance and for good reason. With four weeks of paid vacation, frequent teambuilding events, ability to work from home (laptops are provided for all), and 9-5 the norm, the work environment is great if that's what you're looking for.
Cons
If work/life balance is not what you're looking for, the pay-off of relatively low salaries is not that great. You'll get paid about 25-50% more in comparable jobs in other financial services companies. Decision making is also incredibly inefficient and slow due to the corporate culture of "alignment" (which basically means that no one wants to take ownership of projects/initiatives) and the highly-matrixed nature of business units within the company.