Although her thesis is a bit late (unless you are a Christian of a certain type, the fact that Christians destroyed or transformed much of the ‘pagan’ classical world is no longer a surprise) this is still an interesting book, especially for people with no background in this area of study.
But there are problems. One flaw is that Nixey repeats herself a great deal, basically telling the same tale over and over. There is little variation in the work, to the point where one feel the urge to skim. A shorter book, or even a long paper would have been far more compelling to read.
Another flaw is that while Christianity is given some, but little, credit for saving works from the classical world, it is held completely responsible for the total loss of classical works. Surely this is not true. Much was lost from wars, fires, neglect, social and economic breakdowns. Works from antiquity did always need Christians to hasten their disappearance.
Finally Nixey present Christianity in dark tones, hence the title. But was it really as dark a force as Nixey account? I think not entirely. She takes some threads from Rome's marriage to Christianity, and from that, makes a whole cloth.