What is the author's tone in The Norse Myths by Kevin Crossley-Holland?

The tone of the book is subjective. The myths read more like fictional stories instead of a work of non-fiction. There is no way for the reader to verify the facts of the myths themselves. However, the history behind the myths can be verified by checking other accounts like those of Snorri Sturluson. The reader is free to interpret the myths as he chooses.