I'll admit it: I don't understand this book. I couldn't tell who was speaking sometimes, I don't understand how the Evas fit (or their relationship to Imp), and I don't understand even whether there WAS a narrative arc, let alone whether it was good. The nonlinear structure didn't help in this regard.
The reason I gave the book 2 stars is because of the writing. Kiernan gets across brilliantly what a disordered mind might be like, and I want to root for Imp because of it. She also conveys a sense of place very, very well. It might simply be the nature of the mental illness that I couldn't find a hook to hang my hat on.
As I said, I don't know what to think about this one. Sorry if this review isn't much help.