The value in this story comes from the fact that there is no real "bad guy" in play -- both princesses love the prince, and he's conflicted for both personal and political reasons, making this one of the more complex retellings of the story. Even the sea witch is not evil or motivated by greed or malice: she warns Lenia (the young mermaid) that it is a terrible thing to lose a part of oneself, but leaves the choice ultimately up to the mermaid princess.
The book was shorter than I expected, given the complexity of the situation, and I found the writing to be overly formal. On the other hand, since it was adapted from Andersen's story, it makes sense that Turgeon would use similar language. Turgeon does give the main characters complexity and depth, but I would have liked to see that from a few of the other characters, and would have appreciated a little more world-building. There are hints of it within the undersea kingdom, but it's never filled out in the story.
It has the same problem that all versions of this story have to a modern audience: a young woman giving up her life, family, and greatest asset to be with a man (who doesn't even know she exists). Turgeon does manage to give Lenia something else to live for in the end, and this becomes more of a story about two women saving each other than a romance or a story of a heroic prince or tragic princess.