The premise - revealed pretty early on so I don't think this is a spoiler - is a bunch of people leaping from body to body in Quantum Leap style, but rather than back and forth within history, between an infinitude of parallel Earths. Banks has an unusually powerful imagination, and he's used it to render each world with depth of detail in a quick vignette, rather than to produce a shallow cavalcade of implausible exotica. The writing too is controlled and lyrical or cynical as it needs to be. Avoid of course if you don't like reading about sex, torture, or politics.
I am less than a third of the way through,and I might do a longer review when I have read the whole thing.
Incidentally, I think Iain Banks is a writer who works well in audio format, while other very good writers (for instance Ian Rankin, in fact the crime genre in general) don't seem to come across quite so well. I enjoyed 'Matter', on audio, more than many readers. I don't know if this partiality has influenced this review.