Pros
Multi-cultural, inter-disciplinary staff which makes for some of the most engaging working environment. Good exposure to international development in many fields. Great opportunity to travel to developing countries in engaging ways. Many opportunities for career advancement only with the right (past or continuing) education - experience alone is not as valued. Great pay and benefits (even though they have decreased since the late 1990's)
Cons
If you are dedicated and hard working, the organization will quickly hone in on you and unload all the work not done by the less productive staff - then work-life balance is close to non-existent. The work can also be overwhelmingly about pushing papers (red tape). It is a huge bureaucracy run by bureaucrats and politicians; so despite good intentions from operational staff, the work is often slow, inefficient, and frustrating - some might argue incompetent.