Pros
You get to do meaningful work to prevent the abuse of animals in our society. There's no better feeling than ending a day knowing that you've made a difference for dogs, cats, wildlife, farm animals, and more. Most of the management is very mission-driven and devoted to creating a positive work environment for everyone. There's a Women in the Workplace task force that exists to ensure gender equity and a collaborative work environment. The vast majority of managers and VPs are women, and while several executives are male, they work hard to ensure everyone's voice is heard. Overall, it's just a really great organization.
Cons
It's not a "normal" job, in that there's always more to do. If you wanted, you could work seven days a week and would likely be rewarded for it, which creates some work/life balance issues. But such conditions vary by department. Some managers expect more than others.