I only started reading it Wednesday last week, polishing it off by Monday isn't bad at all. It's understandable though: on this evidence, Kate Atkinson is a really good, compelling writer. I'm not going to post a proper summary/analysis here – I'm sure there's plenty of that online already – but for posterity, and for my own reference, some stray thoughts:
I loved all of the characters in Case Histories. Character is what Atkinson is all about. The various strands of the story proceed in fits and starts, rubbing up against each other and interweaving, but they're always related from the perspective of a particular character. Not in the first person, mind: Atkinson writes here in the omniscient third person. But she does get inside the heads of her characters brilliantly, so that a lot of the events in the book are related by people looking back on those events and attempting to interpret them, or experiencing them now and trying to interpret them as they go along, with all the intellectual and emotional muddle that entails.
Towards the end of the novel, unexpectedly it becomes really funny, so much so that I laughed out loud a couple of times. Jackson in particular comes into his own in the second half of the book: he's increasingly put-upon and disaster-prone, lurching from humiliation at the hands of his ex-wife and her new partner, to being mugged (or not, as the case may be), to having his house blown up – a turn of events that stopped me in my tracks it was so unexpected – much of which results in repeated trips to the hospital.
The final revelations of the three main case histories don't come as much of a shock; I'd guessed most of them by that point anyway. But that doesn't matter: as ever, it's the journey that's important, and Case Histories is a winding, complicated excursion in the company of a disparate bunch of messed-up people who you nevertheless really wouldn't mind hanging out with again.