World of Darkness, and especially Werewolf the Apocalypse novels aren't uncommon. However, one issue they all tend to share is a very varying view on the setting. While minor omissions and mistakes can be forgiven, there are times that the novels' world does not match the Werewolf-setting enough for the reader to understand things in context.
This is not the case with Song of Unmaking. The book takes pains to include things important to the Werewolf the Apocalypse setting and make sure they all matter. The Litany is there, Rank among the garou is there, as are challenges. The reader can easily use their knowledge of the setting to understand the gravity of each scene and the politics present in the sept the story is set at.
However, if the book was just accurate to the setting, it would at max get three stars from me and mostly because setting accuracy is so rare. But Song of Unmaking is also a good story, using the setting material masterfully to craft the story, rather than be hindered by it.
The motif of the novel is loss of a loved one and how grief can drive a person to do awful things. Both One-Song and Czajka have spent years trying to escape their grief in unhealthy ways, and both have to face their faults by the end. The novel does not point fingers on either, however, instead showing how one can heal from their trauma. Or how toxic people can make use of your loss to their own ends.
In the end, even if the book has a lot of violence and gore, the Unmaker and how it is defeated are both spiritual.