Pros
Above-average benefits, good pay, very good location in DC. Many of the employees do care about the mission and are reasonable to work with. And the mission of the organization to serve others, especially those 50 years old and older.
Cons
The only thing keeping this organization afloat is the large membership and the lack of competition. There hasn't been a substantial contribution to society from this organization in decades. They celebrate little accomplishments and minimize the failures. It is incredibly difficult to get projects done or to get anything through Procurement. When they want to get rid of poor performers, they re-org and eliminate positions. It is very top-heavy, with probably a quarter (or more) of the staff either Managers, Directors or VPs. There are a ton of VPs, some having only one or two direct reports - hardly anyone left to actually do the work. Decisions are either done by consensus (please everyone) or by senior management who don't have enough information but think they know everything. Lots of turf-protection and lack of coordination between groups.