Pros
Unique among other specialised agencies of the UN in that it is a tripartite organisation (government, workers, employers) and therefore the experience you can gain on thematic areas/levels can be quite rich.
Cons
Life as a young professional here sucks. The way you try to break-in is through external collaboration (consultant) contracts which means perennial precarious state of employment (how ironic!). Getting into P-positions is quite a challenge if you're not from a JPO-financing nationality. Most positions are pre-cooked, i.e. they advertise but already have someone preferred for the position (reading between the lines in the requirements usually gives it away). The entire organisation works at snail-pace with few motivated people. Most are just happy to be risk-averse and not innovate while enjoying the great salary and additional perks. If you want to end up being a "mediocrat", this is the ideal place.