Orson Scott Card has always been an exceptionally talented writer - right from his 'this is my Master's thesis' Hart's Hope. He doesn't always pull it off - I've skipped some books and not enjoyed others - but there's no question he knows what he's doing.
Card is particularly good at YA stories, in part because his characters speak to children as if they're intelligent beings. That's the angle he shoots for here, and he largely hits the target. The protagonist is a credible teen, and his friends are credible teens, especially because they don't talk like typical fictional teens; they talk like young people who think.
Card doesn't get everything right. Ezekiel's father is way too accommodating and cool to be credible, and there's a bit too much clever banter. While the dialogue and emotions are often deep, the plot is fairly shallow - in fact, it feels like a plot thought up by a young adult; a bit simplistic, with far too much coincidence. That's a good part of what keeps the book from being more enjoyable, and it's odd, because Card is a remarkably well-rounded writer, and can plot with the best of them.
There are also some throwaway comments that undermine the book's claim to being interestingly philosophical - such as a brief riff on how Ezekiel's father, a butcher, is too sensitive to actually kill animals - but just fine, apparently with mocking people who don't actually eat animals. I guess that so long as the blood's not directly on his hands, everything is cool. Card's personal philosophy - with which I heartily disagree - shows through in a few other places as well, but not quite so blatantly or hypocritically.
In short, a good book for intelligent teens, but marred by sloppy plotting that keeps it from being as good as it could be.