I listened to this on audio, unabridged. The whole thing is about 15-16 hours long. For the first three hours - so a considerable chunk of the book - the emotional tone is very restrained, and frankly almost nothing happens. I had two or three books on the go, and I was dipping into this in breaks from the others, take it or leave it. Then at 3 hours it suddenly ramped up. I can remember, I was walking down Canley Ford, when the whole story suddenly broke open in a shocking event, and I could hardly bear the rising tension. The writing was very controlled and perfectly paced.
A voice reading a story in your ear is very intimate, particularly lying in bed in the dark, and towards the end of the novel, as things become more spooky, I had to sit up and turn the light on because it was insinuating and scary.
I can compare this to her previous 1940s-set book The Night Watch - a step change in improvement in writing quality from her earliest novels, and you feel you are in the hands of a professional who is completely in control of her craft. Having said that people might find it a slow burner, and some might be frustrated that it isn't explicitly one thing or another. Personally I'd like to see it Booker-shortlisted.
Oh, yes, and one more thing. If they put this on telly I'd like to see David Mitchell as the p.o.v. doctor character. I think comedians play horror quite well. Failing that, perhaps Mark Gatiss or one of that clutch.