Either Card should have begun his book later, and assumed this as backstory, or fleshed it out more. The relationship between Diko and Hunahpu develops over the first half of the book, but still we don't get enough of a sense for their feelings before they leave for the past. Whether I agree with Diko or not, I still felt that Card was putting one of his puppets through its motions. Namely, that the Other can be Human. However, despite my suspicions, Card still pulled off quite a number of believable character moments, and this is the backbone of the book.
Card fills the book with many fascinating ideas and speculations.
As I already mentioned, I think that it's unfortunate that he forced the question of changing the past with the fact that the future is rapidly becoming unlivable. But the attitude among the Pastwatchers that the suffering of the past matters always reminded me of Slaughter-house Five , a complete contrast. It's as if the Pastwatchers are unmoored from their own time, but come to the opposite conclusion and decide not to take refuge in the happy moments. I liked the careful way Card makes the new humanist era a product of both Carib and Spanish cultures, along with the guiding wisdom of the age that did away with itself. Columbus has to learn that there is a basic difference in attitude between enslaving the natives and converting them.