I came across Before I Fall in Foyle's on a trip to London, and had a flick through before deciding I wouldn't bother buying the trade paperback edition. However, it stayed in my subconscious enough that as soon as the standard PB edition came into work I knew I had to buy it.
It sounds as though it could get dull; I have to confess to starting to lose interest in Harry Potter and the Prisoner of Azkaban (otherwise one of my favourite books in the series) when Hermione introduces the time-turners. In Before I Fall, however, there are enough differences in each version of Sam's fatal Friday, trying to avoid her death, to make it thoroughly enjoyable and not at all repetitive. In one version, for example, Sam and her friends decide not to go to the party. The genre-savvy might think they know what happens next - but there are different shocks in store.
Throughout the novel, we see the consequences of seemingly insignificant events: which car park they use at school, or where to go on their lunch break, the effects of skipping various classes and which events happen differently as a result. Though the same day is repeated for Sam and the reader, the story progresses in a linear way, as her character mellows from a rather selfish, unsympathetic character to someone much gentler. Also, character relationships change over the course of repeated days. I found it very satisfying to see how small events and peripheral characters come together to be crucial to the end result. Before I Fall is a fascinating exploration of what happens when you make different decisions. I can see this becoming a big hit, like The Time Traveller's Wife, The Lovely Bones or Jodi Picoult, and am wondering how long it will be before it is made into a film.