It contains a good amount of all of the essential amino acids (ie the amino acids that your body cannot produce adequately itself). It also has calcium and iron. It's a pretty awesome nutritional food.
EDIT: to emphasize, the key advantage of quinoa is that it has a lot of all of the essential amino acids, which is very very rare among plants. I believe the only other plant with all essential amino acids is soy.
EDIT: to emphasize, the key advantage of quinoa is that it has a lot of all of the essential amino acids, which is very very rare among plants. I believe the only other plant with all essential amino acids is soy.