Pros
The mission (though for those who have spent their lives working at different mission-driven orgs it's not the only one out there with a great mission). No worry about fundraising or resources: the money is there. Lovely campus and great benefits. Some nice co-workers. Great door-opener and looks great on resume. Smart people. New CEO does seem to at least be raising the right questions though it is tough to change this place.
Cons
Exceptionally bad management. Frequent re-orgs. No mentorship, very little chance to move up. Employees are mostly unhappy and morale is awful. No transparency about decisions. Very old school top- down, passive aggressive Pacific NW culture, like MSFT or Amazon. Most people leave in about 3 years and those who stay have made survival their primary purpose. No one really challenges the founders and there is an aura of fear around "what would Bill say". For an organization that works mostly in developing countries or to improve poor public schools, there is very little diversity in staff and certainly in leadership.