Pros
Good salary for experienced people, benefits package ok. Relaxed dress code and quite flexible on working hours. Nice working environment (though completely open plan can be quite a distraction when you're trying to write code), free drinks and snacks in the pantry. Senior programmers do get some freedom to determine what work they do and how it gets done.
Cons
Poor codebase and development tools creates a maintenance nightmare, you can find yourself spending more time firefighting and working around inefficient old code than creating new apps. Culture changed a few years ago to a 'metric' based system where you get rewarded more for ticking boxes and saying 'yes' to the right people further up the management chain (don't believe anyone who says the company has a flat structure - there are 8 levels above mine and this is typical). Coupled with their philosophy of mainly promoting eager to please, inexperienced graduates this has led to whole layers of incompetent mangement led by similar, more senior managers who have no industry or engineering experience other than at Bloomberg. The only way of improving your prospects is by enrolling in a 'leadership' course led by the very same people, few people are promoted based on ability. There is no distinction between project managers and those with the necessary people skills to manage groups. Pension is not particularly good. Used to be able to work from home occasionally but now this must be approved by senior managers, just one example of the atmosphere of mistrust which had led to a general atmosphere of low morale.