Despite the many issues, I'd still suggest anyone interested in the Aztec empire at the time of the Spanish conquest to read The Conquest of New Spain by Bernal Díaz del Castillo. Díaz was present not only on the Cortés expedition, but on the earlier expeditions led by Córdoba and Grijalva.

The article mentions, plausibly so, that the issue of human sacrifice was often exaggerated by the Spaniards. Nevertheless, it is clear that the practice (and self-mutilation, primarily of the ears) was an important aspect of not just Aztec life, but many of their neighbors' as well.

Díaz writes, "I have spent a long time talking about the great cue of Tlatelcoco and its courts. I will conclude by saying that it was the biggest temple in Mexico, though there were many other fine ones, for every four or five parishes or districts supported a shrine with idols; and since there were many districts I cannot keep a count of them all. [...] Every province had its own idols, and those of one province or city were no help in another. Therefore they had infinite numbers of idols and sacrificed to them all."

Discussion of deities and their numbers aside, Díaz' repeated report is that sacrifices of various sorts were widespread, and that evidence of human sacrifice, or the holding of prisoners intended for sacrifice, was found almost universally from the coast to Mexico.

Edit: Reading again, on the subject of tzompantli, or a similar arrangement for sacrificed remains, Díaz writes, "They strike open the...chest with flint knives and hastily tear out the still palpitating heart which, with the blood, they present to the idols in whose name they have performed the sacrifice. Then they cut off the arms, thighs, and head, eating the arms and thighs at their ceremonial banquets. The head they hang up on a beam, and the body of the sacrificed man is not eaten but given to the beasts of prey."