Pros
The organisation is really at the frontiers of international development Research conducted here is absolutely top notch. It's a huge organisation with lots of departments and units with a diverse roles and its very easy to move from one to the other. Very talented and smart people. Very easy and quick visa sponsorship.
Cons
Most of the employees are hired as "consultants" or "temporaries" with very low wages, no health insurance, and no other benefits. Almost all entry level positions are either consultants or temporaries and it can be very difficult to move your way up the hierarchy. If you are a consultant or temporary and your boss is not nice you can be blatantly exploited and made to work for way more than you are paid for. Most consultant/temporary levels are part time and under the G4 visa regulations you have to reenter the US every 90 days which is horrible.