Pros
FactSet used to be a company that people would stay at for years, but things have changed. It has grown and does not have the same small company feel or growth. Management is more concerned with satisfying the market and stockholders over investing in the long-term future. If you are out of school, it's a great place to get a job, learn, gain exposure to great clients, take your CFA and move on (don't stay more than 3-5 years regardless of what you are promised). Life/work balance is great as are benefits (lunch, insurance (keep in mind if you don't have a family the insurance isn't as valuable), CFA payment, vacation. People are also nice though you don't always get a sense of what is really going on, very hush hush and no one is direct.
Cons
Management is very keen on quick fix to keep profit over any big changes that will help the company long-term. Pay is below market. Middle management is a mere messenger, they do not have the power to really do anything else.