I have never read a Hercule Poirot book, and I have not seen the movie version of this Agatha Christie classic. Thus, this is an untainted review. Let me go ahead and solve the mystery for you – this is a very fun book. It’s especially fun if you get the audio version narrated by Dan Stevens (Downtown Abbey et al.). 
For the other three of you who haven’t read this bottle episode of a mystery – famous Belgian mystery solver Hercule Poirot is on a European train ride when the train gets stuck in snow and…someone is murdered! I can’t imagine why you’d murder someone when a famous detective is like nine feet away. That is poor planning.
Using his Holmesian powers, Poirot interviews his dozen fellow passengers to determine whodunit. These travelers include a silly old American prone to hysterics, an imposing and remarkably ugly (not my words!) socialite, some sassy butlers and valets, middle aged military men, and a mysterious single woman. You can see why Dan Stevens’ reading would be so much fun. I laughed out loud in several sections. He seems to relish laying on the accents and affectations in this little melodrama.
They mystery itself threw me for a loop. I couldn’t wait to write in a review that I solved it before Poirot did, but all of my hard-boiled experience didn’t help me, much. I some ideas, but I never quite got it until the end of Act 2. That doesn’t even count as solving it, because Poirot has already laid out his notes twice.
This audiobook is only six hours long. I recommend it. Not a bad way to spend your commute for a week!
Agatha Christie really is a legend when it comes to mystery for a reason. I can’t think of a single of her books where I’d figured out the whole mystery before the end. To be fair, she herself admitted later in life that she didn’t always plan out in advance who the killer was, she went back and edited the book for the pieces to fit once she’d written the ending. :)