Pros
Generous vacation accrual: 2.5 days a month for fixed term and 1.5 a month for temporary employment. Decent maternity/paternity leave but many corporations offer better packages. Sick leave is very good - depends on the years of service - but can last for several months at full pay. Education expenses are subsidized but cuts (in many areas) were made by the General Assembly in January 2016, so it remains to be seen. Good quality self-funded insurance plans but see cons below.
Cons
US citizens are not treated equally in pay and benefits - a cautionary note to those in the US interested to work for the UN. US citizens in professional categories will receive about 10K+ net less because the UN requires US citizens to pay part of their federal taxes. No relocation, rental or home leave benefits either. Unlike in the corporate world, your pension contributions are mandatory, even when you start on a temporary basis, or if you are lucky enough to have a trust fund and arguably do not need to save more. This is driven by the fact that the pension fund is under pressure to honor its obligations to retirees and funds are diminishing, not unlike US local governments, mind you. UN has no COBRA benefits, which means that if one separates from the organization, the insurance is cut off.