Pros
Great mix of people from all over the world with a common mission - to help improve the lives of others. Interesting projects, incredible global reach.
Cons
Travel: this can get absolutely exhausting and be taxing on health/family life! Bureaucracy: it takes a lot to get things done, partly because of risk aversion/a culture of not wanting to take calls on difficult decisions, but also just because its a 13,000 strong behemoth with operations all over the world. Politics: Getting promoted isn't just about merit - a lot of internal politicking, which isn't fun if you are not that way inclined. Pay: Less than private sector (especially if you come from a finance, legal type background). The benefits are great (if you are staff - terrible/non-existent if you are a consultant), but they have been whittling down the benefits package over time, so if you joined recently, its not as great as if you joined say 10 years ago.