Pros
Professional development is good, company invests in its staff. One of the biggest companies in international development, which means there is a wide variety of technical areas, geographic areas, etc. in which to gain experience. Good reputation externally. Most staff are very friendly and willing to chat with and mentor junior staff, easy to make connections internally.
Cons
Some departments have frustrating, arbitrary rules about promotions and pay raises. But the departments can make their old rules here - which is also frustrating. Junior staff are overworked and underpaid, senior staff make a LOT more. Once you’re in you get set raises (usually 3-5%/year) so it really pays to have previous experience at a higher rate. Women tend to make less money than men and get promoted more slowly. A lot of senior management is old white men who have worked there for decades.