(I got an ARC through NetGalley, in exchange for an honest review.)
Perhaps not the most original thriller ever for someone who's read a lot of such books already, but for me—since I seldom read that genre—it was an interesting story. Guessing who the culprit is turned out to be relatively easy, but this book is of the kind where the whodunnit doesn't really matter: it's how it happened, how and why the person got there, that is the most important part. The fact that the narrators are all more or less unreliable, especially Rachel, also add to the confusion, in a good way.
The story is told in first person, from three women's points of view, and each of those give a different insight and different sorts of tidbits, allowing to piece things together gradually. They're all flawed protagonists in their own ways, and this can be seen as either annoying or fascinating, depending on where you stand on the matter. Sometimes, they seemed pretty weak and clingy (as in, being unhappy about their lives but not exactly doing much to change things); on the other hand, I guess we all know that big changes in general aren't so easy to enact as it sounds, and so those protagonists are both relatable and slightly grating, because they might force us to face some problems of our own. (Had I read this book during another period in my life, I might have been uneasy, feeling like I was confronted with things I should be doing, but wasn't.)
Whether one ends up liking or disliking the protagonists doesn't really matter, because it's clear they aren't meant to be a hundred percent likeable, and that their roles are never all black or all white. Rachel's alcohol problem and disturbing voyeuristic side (watching people from the train, imagining what their lives may be, then wanting to make her own place in those lives...). Anna who acts all righteous but who still was the proverbial bull in a chine-shop. "Jess" whose boredom is understandable, but who also twists truths in her own narrative. "Jason" who may not be such the perfect husband. And so on.
I would probably not call this book "the next Gone Girl", though... but then, I don't like comparing novels in general in such a way. This one stands on its own.