Pluspunten
Excellent people with high levels of education and background to bring new views into your work. Very friendly and open culture. Almost anyone you email and ask will meet you for coffee and talk about their work. Lots of opportunities for networking. Tons of interesting projects, although it depends on your area. Looks great to other employers on the resume. Yo will love the cafeteria, the gym, cultural activities, people, Te IDB has their own credit union.
Minpunten
It is a Spanish speaking environment. If you don't speak Spanish you will have a hard time. Just be aware that very few Consultant move on to be staff. This is not really a downside if you're not counting on it, but a lot of Consultant spend a ton of time there waiting for a staff position that will never develop. This always seemed pretty clear to me, but some people hate it. For those who do make staff it's a great job, but there's relatively little room for advancement within the organization.