If you are a person who likes to be an independent contributor, technologically focused and be given some free reign on your projects -- actually, I'll go out on a limb to say that if you are a decent programmer, who expects a disciplined approach to programming (most of the code is haphazard and difficult to maintain) -- this company may not be for you.
Bloomberg has a lot of ridiculous bottlenecks that would make any sane programmer cry with agony. I'm not understating this, you can get the hints from all the reviews up there before mine (at the same time, I'm surprised at some of the 4 and 5 ratings here!). These bottlenecks/annoyances are not just in your day-to-day development, but while you are in the building too.
The badge-in/badge-out, the security making rounds around the office who stop you and sternly ask to wear your badge -- even while you are just going to get a coffee in the damn pantry (I've had to literally go back to my desk to get it), I encourage you to visit the premises talk to existing employees beforehand and get an idea of what you are getting into.
No proper cafeteria area to eat your food -- the running joke was that the bigwigs expect you to eat at your desk and thus you will be around your desk to be called upon by your manager/peer during that time.
You might end up in teams (from what I've learnt, this is most of them) where there is rampant micromanagement (including hints dropped about you expected to work on weekends/late hours to make an arbitrarily set, extremely tight deadline -- even for internal projects)
I believe that the "thought worker" who takes pride in his/her work can't thrive in cultures [sic] like Bloomberg
