Pros
Great benefits - everything you can think of, including 401k matching, food & snacks, etc Very stable company - even during the last financial crisis they never fired anyone (or so I was told) Great office - Lexington 731 is probably one of the best looking offices in NY, if not the best one. Prepare to meet famous people:) Nice people - generally people are really nice and helpful. Many know each other for years, if not decades.
Cons
You will be working with very professional, nice, often very experienced but mostly mediocre people. Prepare to work with in-house technologies created by those people. You will spend years acquiring non-transferable knowledge (comdb2 anyone? Or maybe a spoon of rapid+?) that nobody in the industry cares about. Eventually you might find yourself in a situation where bloomberg is the only company that is willing to pay you for your outdated/deteriorated skills. Welcome to the family. At least nobody will scold you of your project takes 3 times as much time as planned for no reason. You might even get a promotion, if you worked for the company long enough.