The UN Secretariat is a massive bureaucracy run by professional international civil servants. It is a highly structured and rule-driven environment.
Pros: great benefits for staff. permanent staff have good security.
Cons: difficult to adapt to organization.
The UN Secretariat may not be everyone's cup of tea. It is an interesting place to work because of the international character and the proximity to the General Assembly and Security Council and diplomatic activity.
On the other hand, it is governed by a vast accumulation of resolutions, information circulars, and staff rules. This can make it difficult at times to make change.