A fascinating books series that would actually work quite well even without the adult content (but wouldn't be nearly as much fun or surreal).
The world Zacharias has created for us is the "male dream" in almost every respect. Men of substance (the aristocrats) buy and sell sex slaves at their whim. The slaves are all young, beautiful, skilled, and uninhibited. Men have total control over their slaves, with no responsibilities at all; the main character belongs for a time to a man devoted to torturing his slaves in excruciating fashion, and no one thinks the less of him for it. When slaves become too old to be pleasing as sex slaves, they are discarded (worked to death in short order as "work slaves").
Zacharias makes this world believable, through use of detail and a very-well-thought-out plot that immerses the reader slowly in the various levels of this society over the course of the first four books, and then shows it subject to change in the fifth. As a man, it is rather uncomfortable to see the dark side of the male fantasy. I'm hoping that was a purpose in writing the books.
Not just the story is good, though. The writing, and especially the dialogue, make these books an enjoyable read just for the language. Highly recommended.
(review of free book)