There's a very delicious underlying tension to Paula Hawkins' debut, The Girl on the Train. In a way, it's very subtle that it makes everything mysterious. 
 I think the novel's strength isn't really the twists and turns of its plot, but just that underlying intensity, that psychological battle illustrated by the three completely unreliable narrators. The intensity, the uncertainty all translate from the pages and provide you with this tiny feeling of anxiety and curiosity, where you want to know what's exactly going on. I think it also helps that the characters are in a way unlikable, they're all morally wrong in certain aspects. Their undiluted immoral thoughts and actions present you with lots of doubts about their roles in the story. It presents the question of how exactly can you trust the judgement of a character when you know that they're morally corrupt? Basically, how well can I trust you if you're always lying or cheating or doing something that's clearly wrong?(view spoiler)[and you see this clearly illustrated with how the police take Rachel's testimonies (hide spoiler)]. 
 So what does Hawkins really invite us to do with this novel? She lets us be the judge, jury and the executioner, as only we know what exactly goes on in the minds of these three protagonists. She weaves her tale in a slow pace, building up anxiety, allowing the reader to come up with their own decisions, conclusions on the outcome of the plot. She gives you unfettered access to the minds of her characters. You know their thoughts, and though the timelines and incomplete pieces of the plot are there to deter you from your path of judgement, you can start to decide exactly what kind of characters she creates. Are they good? Are they bad? What makes them the way they are? Is it their desires? Speaking of desires, can one truly go after what they want without taking into account the consequences it might have on others? Most importantly do your desires shape and mould you? Who are you really? What makes you? 
 The Girl on the Train is a delicious gripping thriller that keeps your mind active and guessing on where exactly the train/story is going to turn.