If you haven't read Book 1 & 2 of the Troy Game, read them first. This isn't the sort of fantasy trilogy you can just hop onto. In fact, if you read God's Concubine when it first came out it might be a good idea to reread it before jumping into the third volume. Unlike Book 2, which eased into the conflict, Darkwitch Rising leaps into the plot and pursues it in so many different places, with so many different reincarnated characters that it is difficult to keep all the identities clear.
Still, if one keeps on reading there is a great pay off. Douglass' narrative is so intricate that there are surprising twists and turns in almost every chapter. Plot wise, the Troy Game is one of the most intricate fantasy epics you will find. Sara Douglass is impossible to predict and the layers of surprises are amazing (some work better than others -- switching around two characters for example opens up way too many questions). The beginning is slow, but from the moment the character of Catling is introduce, this book finds its way.
Douglas' characterisations are a little more problematic. Often the characters seem to act in a certain way simply to allow a surprising plot development to happen. The reader is therefore more engaged intellectually than emotionally. Reading the book is like watching someone solve a rubix cube, but as satisfying as that is, a little more emotional investment would have made the tale even better.
For example, PLOT WISE, it was interesting to see Noah/Caela/Cornelia fall in love with a character she previously loathed, but EMOTIONALLY, as a reader it is difficult to accept how easily she forgives the atrocities he has commited toward her, women who he whored and raped, and entire civilisations which he caused to be slaughtered. Explaining it away as 'you had a bad childhood' doesn't quite work. One of the best things about Sara Douglass' writing has always been how the ideas of good and evil are very flexible. In her Wayfarer Redemption series the character Wolfstar had killed dozens of children and yet Douglass made us sympathise for him at moments.
However, in that narrative, Wolfstar's actions came back to haunt him. In The Troy Game so far (who knows what will happen in Book 4) many characters commit rape, genocide...etc and then their actions are forgotten or dismissed. In Darkwitch Rising Noah seeks to heal all wounds, and while the wounds of many characters are healed, one is left questioning 'what about all the wounds they have inflicted on characters not central to the Troy Game'? Resultantly, it is sometimes hard to sympathise with the characters. The way that every character in every direction is becoming a god or similar being is also a little grating.
However, overall, this is still a great book. I still feel God's Concubine was a highpoint in the series so far but this is a worthy successor. All the pieces are coming together and this book leaves you breathlessly anticipating the final volume.