Pros
Comfortable place to work. Depending on department, you can ensure a work-life balance and leave work at home. Competitive salary for nonprofit sector. Unlimited sick days.
Cons
Very hierarchical, so it can be difficult to get people to collaborate or listen if there are major differences in title (or years at the organization). There is little-to-no room for growth unless another employee leaves. While the salary is competitive for nonprofits, there is a very stark contrast between managerial/director/vice president salaries and executives (nor is there any real cap on bonuses for execs). Culturally can be cliquey and, given its size, difficult to integrate yourself. There are some difficult personalities, but no initiatives to help mediate or correct behavior.