It's an absolute hell if you're driven by goals and want to deliver results. There are so many pointless tasks that do not serve anyone and are motivated by political reasons. Employment morale is a serious issue (people not showing up to work, not doing their assigned work), a toxic culture mainly due to staff high ego. You will experience lack of management (there's no management at all). Senior management does nothing to fix employees' issues - lack of decisions, unwillingness to take responsibilities, etc. People backstab each other all the time because there are no quantifiable measures to evaluate staff performance, so that only way to get yourself promoted is through nepotism and favoritism which are prevalent in all levels of the UN. There is no training at all for junior staff. The UN has on value to add to many of the problems they are tasked to deal with - all the reports done at HQ are copy and pasted from Google. The UN is a complete joke, and should be ashamed that it operates on precious donations from Member States. No wonder so many global problems exist, and the UN is losing its ground in international relations!
