Pros
The work environment is reasonably pleasant, although it does feel like a corporate job. You get a desk in an open floor space, but there's plenty of places to find a little "retreat" to think or relax during the day, and flowers and aquarium contribute to making the very glass-like structure more "organic". The kitchen is always stocked for drinks and snacks, incl. late nights and weekends if you really have to stay and finish a project. The Bloomberg annual parties are legendary and really fun (although if they gave us the money they spend on those, I'm sure I'd have been happier - they must be very very expensive!). There are a few perks working for a large employer, like a savings program. My boss gave us plenty of latitude to get the work done, and apart from the occasional crunch time, work was not overly stressful. This varies widely by department though. My co-workers were top-rate. Again, varies widely depending what team you're with. This was my first job out of academia (used to teach before), and although I was an accomplished programmer, I still learned a lot about software and engineering.
Cons
The software environment is both challenging and very peculiar to the company, though. And a lot of it is legacy, which means having to work within a set of constraints (binary compatibility with 1990s Fortran code, code relocatibility, proprietary routines) which I can pretty much guarantee you will not find anywhere else. And because of those constraints, moving code thru to production is a major pain. On some particularly central class I was tasked to optimize, my changes took 6 months to percolate thru to production environment. The bureaucracy is also sclerotic. Having to document your working hours and bill it to various tickets (development, bug fixes, etc.) gets quickly tiring, and meaningless, as the fudge factor for accounting for 8 hrs day makes charging completely arbitrary. Getting a TREQ (technical request for new projects) can be a pain. All this is done thru the Bloomberg terminal which means there is nowhere to hide: your boss (but also pretty much anyone in the company) can find out about all the commands you typed during the day. The terminal has quirks too and I can't count how many times I lost a long typed message because of a wrong key stroke. But the reason I eventually left is that once you're in, the possibilities for raising your salary are limited. You will do well to negotiate the highest you can on entry, it's unlikely to rise significantly after that. Your first year bonus is invested/amanged by the company into internal stock (BB is private) and you only see it in your bank account after the end of the second year (with moderate interests). The value of the internal stock can be tracked using another Bloomberg terminal function, so at least it's transparent. That means of course when you leave they get to keep your current year bonus - the one they are still "managing" for you. This is described by the employer as an incentive for you to invest in the company. The longer you stay, the better. Unfortunately, it makes leaving that much more painful. Until recently, there was an unwritten policy that they would not rehire previous employees. I hear that's been rescinded. Having left all that behind though, I can't really think of why I'd want to go back...