In addition to being an anthropological document, there are also glimpses into the conquistador mindset, motivated by a brutal greed (it is a lust for rumored gold that leads the expedition astray in the first place). He doesn't spare the details of the misery of the survivors, stalked by native archers and beaten mercilessly while on the verge of death, although the episodes of cannibalism brought on by the maddening pangs of starvation are passed over somewhat quickly.
While the narrative of travel is frustratingly vague regarding de Vaca's route, it is filled with details and observations regarding the native Americans he encountered, and must count as the earliest description of these people and their harsh lifestyle. The Spanish suffered many depredations along the journey: de Vaca survived due to his adaptability and no small amount of luck. He found a useful function as a trader among the various tribes, and eventually he and his companions acquired reputations as great healers. His sense of compassion - rare among soldiers of fortune- must also have served him well in his darker moments.
Cabeza de Vaca's narrative is a testament of human endurance and adaptability under extreme circumstances.