Enjoyable, but a bit confusing
The book reminds me of some of today's action movies. Lots of things are happening, sometimes in parallel, with ups and downs, with surprises, with fire, fights, love, sex, chases, etc. In some sense… a bit too much. Too much in the sense that what may work well on a movie, with its visual effects, may not work that well in a book to read where it becomes, here and there, a bit confusing. But… all in all, it works and it is an enjoyable time to read it.
The historical setting is also interesting mainly when one leaves close to the places that appear in the book. I looked up things on medieval Marseille, found references to some places I know, though the setting is still 800 years ago; that was interesting.