Pros
My colleagues at BBN are virtually all sharp, motivated, highly competent and engaged. That's the best part of working here. My experience has been very positive for a number of years-- I've been given a lot of freedom to explore new ideas (within the scope of the contracts we have...) but a fair amount of feedback and encouragement towards career growth as well (in team leadership and business development). (I see in a number of these reviews that people are declaring that "Raytheon will change everything, and you're a fool if you ignore that", but I guess I will wait and see what actually happens. So far it hasn't been a problem at my level.)
Cons
As others have mentioned, the work is largely driven by government contracts. This does mean that there are ebbs and flows, and sometimes you end up shifting to work on one thing when you'd prefer to work on another. There also appears to be quite a difference between the departments, so what a review says about one department might be totally irrelevant to another.