Pros
Great benefits. Good pay. Decent work. Bright, nice people to work with. Very responsive support systems. You will never have to wait for help to get software installed, and if you have a doctor bill that doesn't make sense they have reps that will literally do all the work to make sure you are getting all the benefits you are entitled to. They rock at reducing friction between you and your job. No one ever says "that's not my job" And since its privately owned, the profits go to Bloomberg Philanthropies which champions great programs and brings a net positive value to the world.
Cons
Too few career growth opportunities for mid to upper level roles. Bloomberg is a closed system from a technical and cultural point of view. This creates many lifers who stay for the benefits and are the keepers of the organizational memory (and stability of critical infrastructure) but for curious minds this place can get stale quickly. There are also the usually power struggles and / or rsisyence to change that you see in any big company which create drag on projects in one way or another.