This is a difficult book to review.
First, it's a very slow and difficult read. Just understanding some of the sentences is a challenge - intentionally. Melville wanted to the reader to be a bit uncertain of what he was saying in a few place, so be prepared to take your time with it.
There are a couple of chapters that are downright painful to anyone with modern sensibility about the races. Melville was using the portrayals not because he believed them, but because he was making a point, but that doesn't make them easier to read.
Overall, I found that I walked away from the book feeling very differently about than the reviewer who is responsible for the description on the back of the book - although I understand why he believes what he does about the novel. This is a sort of inkblot test in book form, your feelings about the main character will be influenced more by your own opinions and impressions of the world and how it works than they will be by Melville himself. He created a work that allows the reader to paint it in their own colors.
It's an impressive work, a serious and weighty novel, not for the faint of heart.