Best resources, best learning tools, great/friendly people, flexible hours, great facility. The baby boomers will be retiring soon so NASA will be looking to hire younger people. Also, there are many opportunities available for young professionals to develop from NASA's online class databse to instructors that teach weekly seminars on powerpoint, excel, etc.
Cons
Poor compensation, the work is not challenging enough, the projects can be boring, and the efficiency at which people work is extremely slow (especially when compared to private sector counterparts).
It is great to work somewhere that makes a difference. NASA is trying to make the world a better place to live. The opportunities to make a significant difference are emence
Cons
I would say that the only down side is that the reward system is limited by law. The opportunities to advance are difficult and time consuming.