Pros
Local TNC offices in various states and around the world work on some great projects, and contribute a lot to global conservation of important habitat and wildlife. Coworkers are friendly and most are dedicated to the goals of conservation, so there is a lot of common bond.
Cons
Amount of bureaucracy and hierarchy in the national organization as a whole is staggeringly high. Advice of employees who are experts in their field often seems to be discarded in favor of personal agendas of senior management. Salaries are significantly below industry average. Although that is to be expected when working at a non-profit, it is very frustrating to be working for so far below industry average salary as you watch the money that is not in your paycheck being wasted on bureaucracy instead of going towards the real work of the organization. The work-life balance they promote as one of the benefits of working here doesn't actually seem to exist, and is quite far from the reality of working here. Overall, it's a very traditional bureaucratic and hierarchical corporate culture--in many ways, even more bureaucratic and hierarchical than most large for-profit corporations I have worked for.