Pros
Because of the regional scope of the organization, you get to learn a lot from successes and failures of diverse government agencies in various countries. In addition, I would say it is also very easy to get involved in interesting projects from diverse sectors, provided that you are willing to spend some extra time working on them. Since the workload is not crazy, this is totally feasible. There are always interesting talks and projects going on, so it's definitely a good place for curious people.
Cons
If you work in headquarters (in DC), you can feel far away from those who benefit from the policies you help to shape. In addition, bureaucracy can feel a little slow at times. Projects take some time to take off - although once they do, implementation is very effective.