Many readers found this book engaging. Lippman set herself up with a challenge: the main character may or may not be who she says she is, and without knowing her or trusting her, we have to empathize with her enough to like reading her story. Opinions seem to vary on whether she is successful in making us want to know more about Heather.
I didn't find the book very compelling. Heather was unlikable, and unknowable, and the parts of the story set in the present were tedious. The mystery was interesting, though, and I'm terrible at solving them so I didn't guess the ending before the big reveal at the end. But it was a pretty long haul to get there.