I wasn’t sure what to expect from this book. The premise wasn’t something that drew me, but the fact that so many of my friends recommended it made me curious.
Immediately I was struck by the similarities to Gillian Flynn’s novels (mostly in the writing style and the use of mysterious and unreliable narrators). Not at all surprised to come here and see other reviewers are making the same comparisons.
The storytelling in the novel was tight; Hawkins tells the story at the right pace, in the right order, revealing different timelines in tandem in a way that unfolds the story wonderfully. I figured out the “twist” about halfway through, but only because of her use of misdirection on every character EXCEPT the killer. I wouldn’t say it was predictable, though, and right up until the end I still thought things could shift another direction. Everything feels possible.
My one beef with this story was (and this is also keeping in tune with Flynn), that every character was unlikable, to the point of being grating. I love a good antagonist or antihero. I love divisive characters. But Rachel’s tics and issues became tedious and grating by the end of the book. Megan was an interesting character who warranted further time and explanation because, I suspect, she’d have been incredibly more dynamic than her limited narrative allowed and perhaps more sympathetic as a result. Anna wasn’t given enough page time to separate what appeared to be her sociopathic tendencies vs. her love for her child. And the men suffered from similar treatment. Like in any Flynn book, you walk away feeling as if there is no clear winner.
That said, this book kept me up all night reading, which is rare for me nowadays, so I can’t say the challenges above had a significant impact on my enjoyment. The Girl on the Train is a tightly woven, excellently-paced thriller that I’d recommend to readers who love a great suspenseful read. 5 stars.
...and then there was Sarah 
I too figured out the killer about halfway through the book, but I still enjoyed the writing. I also read the Flynn book, I think called “Sharp Objects.” I loved the relationship between the sisters in that one. Both books are good reads.
I enjoyed Sharp Objects as well.