Pros
Global Zero's staff is young and energetic, and is passionate about making the world a better place. The team generally enjoys spending time together, and this isn't a buttoned up Beltway organization. Work is collaborative, and people are given more responsibility and ownership over work than they likely would get at other organizations.
The organization is evolving and as it grows there is room for new ideas, responsibilities and roles -- there isn't a set path for promotion but rather each individual and their manager talk about the needs of the organization and how that matches where they want to grow. When people are promoted, it's often to a position that didn't exist before, offering unusual commitment to professional development for an organization this size.
GZ offers really generous benefits, better than I've seen at similar organizations and leadership genuinely cares about the team.
Cons
This isn't the organization for someone looking just to bring home a paycheck. It takes commitment to work on a tough issue that's not easy to break through on, but when successful can make a huge difference in the world!
As is true with many issue based advocacy campaigns, there can be more ideas than money to implement so creativity and patience is necessary.