This is the kind of books people adore and hate at the same time. I adored it; I had a hard time put it down. I hated it; it would not let me take my time with it, to savour the style, the plot, the delicacy of the descriptions and the wonderful balance between action and contemplation. This book is splendid. It reminds me of Donna Tarth for its writing. The plot and the "four species" society has nothing to envy to Anne Rice's vampires series (I think I even noticed a reference to that when she describes how Matthew put some things in order in New Orleans). It has the complexity of "the Historian", "the eight" and the sweetness of "Rebecca". Like Proust, this book brings tastes to your mouth and scents to your nostrils.
My only reproach is that the last part (which takes place in the US) is slower paced than the other two (in Oxford and France).
You need to read this book, and fall under its spell.