I think the way Mike Lee wrote this book was the best way it could have been done. Having this book be entirely from the point of view of Nagash would not have as effective at making us feel the atrocities that he committed, because this book was just as much about the fall of Khemri as it was the rise of Nagash. I know some people bemoan the description of Khemri culture, but in order for the reader to truly realize the horror of what he did you have see all the decadence and wealth and watch it be trampled under Nagash's feet in his ruthless rise to power. You have to see the crowded streets become empty as lives become his currency.
And you have to see it from other peoples eyes, because Nagash didn't care about the hundreds of thousands of people he killed to get what he wanted. The chapters we get of him showed us how twisted his mind was, how little regard he had for life he had, and how little he noticed the ruin he was causing. To much of that would have been boring to read, and we would have been jaded to the suffering of the Khemri people, but seeing the ruin that Nagash caused through the eyes of people who cared about the loss of life, who were enraged by it, kept this book from being just another book about the rise of a sociopathic tyrant, and turned it into not only the rise of Nagash, but the fall of the beautiful and rich culture of Khemri.
Of course the culture doesn't completely fall, the good guys win, if only barely, and the other books have more of the fall of Khemri, but it doesn't completely invalidate my point, I don't think so anyways.