It's essentially arguing that Navajo myths and religion are as valid as Christian myths and religion. It sucks that we still need to be convinced of this (we people who make the study of such things our professions, anyway), but I would say it makes a strong argument.
It was pointed out to me that the stories Levy quotes were all collected by OTHER people, and a lot of that collection occurred in questionable circumstances. Also, he makes some assumptions about history that a lot of Navajo would not agree with.
That said, I thought the issues that come up when examining myths and oral histories were fascinating, and it was cool to see it so explicitly addressed.