Why do so many horror films rely on "destroying the graves of the indigenous" to incite a supernatural power? Because every bit of land in the Western Hemisphere was stolen from indigenous peoples and they are buried all over the United States.
This film doesn't have a lot going for it in the monster department. The Skinwalker here seems to combine a rabies epidemic with some kind of werewolf zombie shapeshifter. It doesn't so much come in the night, but through the bite of those who encounter it. And it isn't even the real monster here.
The monster is the way people treat each other on the frontier, and how it turns good people bad. The good deputy kills an Apache who is trying to help. The woman with nursing skills and a good heart is married to an outlaw. The upstanding Mormon takes a child as his third bride. The outlaws help the people in trouble as much as the sheriff does. And children are turned into killers to help defend a city ravaged by plague.
The good guys aren't all good, and the bad guys aren't all bad. It's a place where everyone is both, and that in itself makes up for the flaws in the film.
Keep an open mind, but cheer for the Apaches.
