Very watchable....but also a "slow-burner". The first two episodes crawl along to build up the tension, and as a writer in Radio Times said - you want to shout "get a move on!".
Never even heard of the book.
Slow burner is definitely how I felt about it, got a bit bored and distracted. Shame really as I’ve probably lost the plot now for the next three episodes and won’t bother.