What I liked the most about "Sorrow" is the way it surprised me over and over again. Not just in regards to the plot movement and development of the characters, though those do take unexpected twists at several points. That element of surprise extends to the craft level with things like form, voice, and point-of-view. This makes me hesitant to review anything in much depth, because I wouldn't want to rob other readers of that experience.
What I will say is that the voice of "Sorrow" is absolutely enchanting, something that feels a bit odd to say given the subject matter, but is true nonetheless. It has a dream-like quality that gives the book the feel of a fairy tale in places, like something that's happening on the edge of reality, despite the fact that nothing overtly supernatural ever happens.