Vantaggi
Benefits are top of the line, outstanding. Even better if you're a foreign national and not an American citizen who gets a permanent staff position - then the UN will pay for your housing, kids' daycare/private school/college/university tuition as well. You also have access to take classes to learn one of the many UN official languages. It's a widely recognized institution doing massive amounts of work around the globe. You'll forget what country you are working in because all coworkers are international. You hear more than three different spoken languages all around you every day. It's truly an international environment and it's very unique in this way. The UN walks the talk - all agencies provide paid leave for new parents in some form and length, including those who adopt children, they also have extensive AIDS/HIV awareness and training for all employees which is mandatory... in all human rights related issues, their HR policies tend to match what they preach.
Svantaggi
The environment, like a government institution (but larger), can become very political. It's not always the healthiest working environment in certain offices if the management is not empowering or if there are power grabbers. This is so dependent on the management, unit and agency within the UN. But in general, I learned there are a lot of people who are working long hours - especially the higher you go in level - and have developed bad work/life balance. There are also rumors of many higher-ups having developed drinking problems, but that is really up to the individual, because the UN offers really great health insurance, opportunities to join sports clubs within the network and even short term therapy for those who seek it. For being an international and diverse organization, there is very little training on cultural awareness and competency. There are many personnel conflicts as a result of miscommunication, cultural differences in understanding or expectations of norms... what you'd expect when people from all nations come together and try to work on the same project with completely different cultural attitudes and norms. Americans have to figure out paying US taxes as the liaisons between the UN system and the IRS - it is the biggest pain in the butt you can imagine. And because the UN pays all federal and state taxes, any reimbursements go back to them - which works out okay, but they also get any reimbursements you get from deductions or credits you receive from spending your own money in certain programs, like educational expenses. You also need to submit your own quarterly estimated social security, medicare taxes to the IRS and figure out the balance during tax season - usually last-minute because the UN Tax office doesn't send you the paperwork until the last few weeks before the deadline to file and then physically drop off tax paperwork to them in person to get a reimbursement check through them to pay whatever you were short... basically, it sucks to be an American citizen working at the UN in NYC. They could be better with their telecommuting and flex hours programs.