Ventajas
Its a well regarded bilateral aid organization, but like many, once you are inside its quite depressing. The people in general are very nice. Its a great work-life balance. If you have kids especially, its such a PC environment that you can get away with working from home, tele-commuting, working part time, etc etc. Nobody works more than 40 hours a week. Its a great place to work if you are left wing / liberal. Final salary pension scheme is a huge perk, plus lots of leave.
Desventajas
Very very PC environment, where any views others than those expressed by the average Guardian reader are not tolerated. There is a huge mis-trust of the private sector and a love affair with NGOs. It pays badly. They have a HUGE budget, growing every year, but few staff to spend it. So they shovel money through other agencies (eg World Bank's IDA), and budget support to Govts (who have become hooked on aid as a result). The *only* thing that staff care about (staff who want to get promoted) is spending the budget - impact is mostly neglected, ignored or hidden. Benefits abroad used to be good, (free house etc) - but I understand these are being cut back. Most economists leave DFID for the World Bank etc because it pays better and they get more respect. DFID is a good place for social workers, in contrast. Its hard to get promoted if you are a white man - there is a lot of bias toward women and ethnic minorities and staff from overseas.