This was a really tough one to rate, primarily because I love some of the ideas and parts of the world created in this book, but the ways of expressing that world just did not work for me. There's a detachment to the writing which jangles with its floweryness. Vandermeer is writing cosmic horror and seems to inherit Lovecraft's love of purple prose. This can work and indeed does work at points in the book, but it makes it hard to take a lot of the earlier, more mundane events seriously, and lessens the effect once things start getting weird. The story spirals into horror and the writing is well-suited to the much tighter spirals near the end, but earlier on it just feels unfocused - A tighter 120-page novella would have suited me at least much better.
The link to Lovecraft feels even stronger as the whole book shows interest in some very turn-of-the-twentieth-century talking points - hypnosis depicted much as mesmerism was in the period forms a surprisingly large portion of the interpersonal tension in the book, and the veneration and definition of characters entirely based on their scientific specialities (and the quite simplistic depictions of what those specialities are and the effects they have on viewing the world) - feel at home most with HG Wells and Edgar Rice Burroughs, and unfortunately their use here feels more outdated than updated.
This is not a bad book. The ideas and concepts in this book make it a good example of cosmic horror - Worries about self, control, significance and insignificance in the face of the unknown and the unknowable - And they form the basis of a brilliant film in Alex Garland's 2018 adaptation. Images and scenarios from this book live long in the memory and will, I imagine, outlive my frustration with their delivery, but I would recommend readers try the film, or works with similar themes such as Junji Ito's brilliant Uzumaki, before coming to this.