I inadvertently began reading this without realising it was part of a series. However it's been named a 'side-quel' and I certainly didnt feel like I was missing vital information by reading this before Oryx and Crake - indeed, I'm keen to read Oryx now with some prior knowledge of the universe (and having briefly met Oryx and Snowman). I see the third book is due out in a few months so some good timing on my behalf. 
 The Year of the Flood is a post-ap novel where a future society is filled with gene-spliced mutated animals, a society run by "corporations" who control everything, where the rich are richer and the poor are barely surviving. The world is bleak, dangerous and full of crazy religious cults and equally crazy street gangs who will kill you to sell you for fuel or body parts. A world where people willingly eat Secret Burgers (source of protein unknown).... 
 The novel cleverly shifts between the present - a waterless flood (a highly contagious virus) has swept through the world decimating the population. When the plague hits, Ren is locked in an medical isolation room at a highend sex club, Toby survives by locking herself in a room at the Spa and eating the edible facial treatments. Flashbacks to the past show the women's past history with the God's Gardeners religious cult and the world 'before'. 
 The strength of the novel lies in the "almost-future" imaginings - a world where genetic splicing and modification has gone one step too far. Scary stuff. Definitely an engrossing and sometimes, horrifying read (just how I like 'em).