Pros
I gave an overall rating of 3 stars because CIMMYT does some great work that really benefits poor farmers throughout the world, and many of its employees are very nice and supportive.
Cons
The organizational structure is terrible -- I happened to belong to one (of five) thematic programs, but worked on a project that was led by a different program. Additionally, I worked on the other side of the world from the HQ (where my boss was) in Mexico. These two factors meant that he didn't have a clue as to what I did on a day-to-day basis, and the key people in the other program didn't feel enough responsibility for me to make sure my strong value to the project was known by my boss. As a consequence I was not promoted. CIMMYT gives lip service to work-life balance -- if you don't work 55-60 hours/week, you will not get ahead. In addition, many of the employees are self-centered and only care about publications -- and will behave badly in pursuit of that objective.