"Farmer's greatest achievement, accomplished with brilliant understatement, is to make us gradually realize that our own situation here on Earth is just as mysterious as anything on Riverworld, or that the answer to the enigmas of Riverworld might also be the explanation of the paradoxes of our own peculiar existence here and now. Once again, in a brilliant climax, Farmer demonstrates my pet theory that sf is the only serious literature around these days, because it is the only literature that grapples with the ultimate questions of who or what we are and how we got here."