I wish there were a sixth star available, to distinguish this monumental work from your ordinary everyday Oprah novels, Atonement or House of Sand and Fog or The Shipping News, e.g. Smart people I know put this book down after a few chapters, finding it too challenging and odd. Very smart people I know find it fascinating and memorable. The smartest people I know think it may be the finest book of the last quarter century.
I highly recommend reading the first three or four chapters, and then starting over, once you've mastered Riddley's dialect. Reading it aloud also helps. You will find yourself thinking and talking in Riddley-speak for months afterwards. And you will read it again and again, finding new marvels each time.
I can give no higher marks to any book since Zorba The Greek.