Pros
Good benefits, some cool people, interesting and exciting mission/vision. Education programs, including reimbursements. Nonprofit, so you get to feel good about where you work. Great if you have good self confidence and a basically positive, cheerful outlook, and if you thrive in a very stratified work environment and/or are good at office politics.
Kontras
Though it's a nonprofit, it's got a corporate "feel". High turnover due to poor managers and low company cohesiveness. Poor morale in some units, good in others. Some managers are mean/vindictive, others are weak, only a few are good managers. Very political workplace as you rise in the ranks. Don't work here if you are emotionally sensitive and struggle with self esteem - it can be a snake pit. Be very selective in how and to whom you tell the "truth".