Pros
The people - good people, good mission. It's literally "save the world" kind of work, which makes it really gratifying to work at this organization and want to promote its cause. Lots of exposure to international cultures too - high ethnic diversity of employees and many different languages floating around this office at any given time. Wonderful colleagues and a great network of assistants to help new hires. GREAT benefits.
Cons
People do tend to get married to their jobs here - lots of long hours, but at least you're in good company! New hires - careful to keep up with the work/home balance, because international organizations have around the world, 24/7 demands. The job review evaluation process (midyear reviews and final reviews) can be painful. Often times its building politics based (there are some egos here - but hey, it's DC), or because of your relationship with your supervisor (a good review definitely depends on it). There's no opportunity for a rebuttal of a poor review for your end of year review - once your supervisor has the final word, that's it with HR.