The book was down on Amazon for a few hours today in order to correct an error in its table of contents. As of now it is back up (and a quick re-load on my Kindle app satisfies my curiosity that the typo has indeed been fixed, though it does unfortunately rob people of the rare first edition version of “God, Robot” with the table of contents error. Apologies to anybody counting on that for income ten years from now).
At any rate, if you meant to buy the book and found yourself unable, now you know why there was an issue and can take steps to correct it.
Purchase “God, Robot” here, and decide for yourself whether or not the rave reviews have been earned.