The chapters in W alternate between a fiction about an imaginary island called W., devoted entirely to sport, and chapters giving an autobiographical account of Perec's childhood during WWII. Both stories are told in a very crisp, matter-of-fact tone, but the contrast between the two is striking. Young Perec's shuffling about and hiding, the death of his parents, is described with an almost disturbing emotional distance. All the emotion that's lacking in those chapters is poured into the ones about W, as it becomes increasingly evident that life on the island is a sort of filtered reflection of the concentration camps (it's a bit like Plato's Republic, too). And because the actual details of life on W. are new, the horror and disgust they provoke is fresh. The combination works like a chemical reaction - there is something unnerving and increasingly horrific that seems to hover between the stories. It's very effective.
W is an experimental novel, but it's not cold or empty; the language is very simple and it was a pleasure to read, went very quickly.