Pros
The best thing about FactSet is the abundance of talented people who don't hesitate to help. FactSet considers it's employees it's most valuable asset and the employees invest their time in one another. If you're just starting a career you can't go wrong with FactSet. Aside from that the other "pros" are numerous, including a great culture, good work life balance, competitive compensation and generous benefits.
Cons
The location of the Headquarters is the biggest drawback. Norwalk is unremarkable, traffic in that part of Connecticut is horrendous and the public transportation is challenging at best. Sometimes the necessary formalism is overshadowed by learning, participation and getting things done. This is great most of the time but frustrating when official career advancement becomes nebulous.