Pros
Amazing fund raising ability and incredibly talented staff. Science based organization puts TNC leaps and bounds above other land trusts and NGOs when it comes to advocating for funding for a project. Huge organization with a global reach and great opportunities for advancement but be prepared to move geographically as you move up what is very much a corporate type ladder.
Cons
All the cons of a large organization - slow, bureaucratic, office politics, risk averse, etc. This organization used to be more entrepreneurial and it claims to still be and in pockets it is, but you may have to try to bust through walls to get there. Don't expect to be rewarded for going above and beyond as the incentives for hard work are nonexistent beyond interviewing for a new position and moving up that way.