Pros
Amnesty is a comparatively well-resourced organization where you get to work with many amazingly well-qualified and well-meaning colleagues. The organization values work-life balance, at least to the extent required by European law. My exit interview was focused almost entirely on work-life balance questions. The breadth of the issue brief means you can get to work on just about any issue possible, if you're lucky (and able to game the system).
Cons
Because of the size and complicated structure of the organization, decision-making is not always transparent. Sometimes sections and members get to override staff concern for and understanding of genuine human rights issues, and sometimes staff get to override section and member concern for and understanding of genuine political imperatives. Internal processes can be opaque and dysfunctional. In some parts of the organization there is a tendency to want to do work as it has always been done rather than value innovation.