Zoë's Tale retells the story of the previous book from a different point of view. The first of these types of stories I read was Bully on Barkham Street, a retelling of A Dog on Barkham Street. In both Scalzi's and Mary Stoltz's tales, I found the second book better than the original.

In the case of Zoë's Tale, the author has had a chance to clean up some of the plot points not made terribly clear in the previous story. He also uses a completely different voice, this one a teenage girl. While not one myself, I found this point of view quite interesting to read and the story really worked for me.

I doubt this would work as a standalone book - we are too far into the major political machinations at this point. Also, events of battle and other plot points are only briefly mentioned. I think a standalone reader would be lost.

All that said, I found this a better book than it's predecessor. John Scalzi went out on a limb and tried something difficult, and succeeded in spades.