First and foremost, I will start by stating that I haven't read the graphic novel. It might be the case that some plot holes or dumb ideas presented in the movie are indeed better managed in the comic, however this is a review of the movie and the movie alone, and as such I was deeply disappointed.
Snowpiercer is a sci-fi post apocalyptic movie; a failed anti-global warming experiment bombs spectacularly and the earth becomes a barren tundra where the only survivors are the few lucky souls that boarded the Snowpiercer train, designed, built and managed by Wilford, and obscure philanthropist that in the times before the disaster managed to get enough money to build a worldwide train network and the train itself. The train is a self contained cosmos where a social order has arisen and the passengers from the back (that were originally freeloaders) live a life of misery while the first and second class passengers have plenty to go around (including sauna, clubs, schools for their offspring) all neatly contained in the train.
The film follows the rebellion of the de facto leader of the tail dwellers, Curtis (Chris Evans) as he and his followers march from the back of the train into the very front where the mysterious and seclusive Wilford (Ed Harris) lives. On his way he discovers many of the secrets of the train and we as viewers also find out what the hell is going on.
People die, hands are chopped of, prisoners made and killed, sections of the train left behind as is all coherence and logic until our goodie two shoes Curtis gets to the final door that holds Wilford at the head of the train. He has a deep and meaningful conversation with the japanese security technician that has been opening doors for him and we find out the origin story of the tail dwellers and how Curtis isn't a paladin of goodness as we thought he was. He delivers his confession of past crimes while smoking the last cigarette on earth, well, taking one puff and then letting it burn by itself. There is the final confrontation between him and Wilford after some more gratuitous violence and the movie ends as should all movies that want to please audiences that haven't fully understood what has happened: with a sort of happy-open ending.
I will go for a wild guess here; the comic book in which the movie was based goes either into much more detail and solves some of the incoherencies of the movie or it is much more symbolical and doesn't dwell too deeply into trying to explain everything; it's an allegory, and as such we are expected to activate our willing suspension of disbelief. No one will criticise The Odyssey for being illogical, the poem is not about how getting lost for 10 years in a patch of sea that should take 2 weeks to navigate is almost impossible, it's about human nature and morality. And no one will criticise Newton's Principia Mathematica for being boring and not making a good story, the book is about explaining the principles behind the way the physical world reacts.
I know it's unfair to compare a low budget sci-fi movie with Chris Evans and Tilda Swinton to two of the most important written works in history, but the movie falls right in between the two of them. It isn't well thought and logical enough to create a believable world and it isn't evocative enough to make us brush aside the inconsistencies to ponder the moral questions it puts forward. The moral questions by the way are pretty dumb in themselves and do not resist the most tender of inquisitions, let alone more deep questions that make the supposedly deep movie show it's true puddle depth.
We are left baffled and dazed at how it is possible for the train to really keep on working and moving forward. How on earth did Wilford secure the money to build a worldwide train track that makes the train go around the earth once a year? I'm no economics major, but that must've cost a lot of money, more than Bill Gates and Donald Trump could put together. Besides, this tracks must've been built before the global catastrophe that made earth go into a new ice age, at that point it must've sounded like a pretty useless project. Why does the train need to move around? wouldn't have it made more sense to leave it's perpetual motion engine inside a huge building where there would be more space to house people and animals? If you have a perpetual motion machine, why don't you build a few of them and keep alive most of humanity? Is it a good idea to keep a wagon full of axe-crazy maniacs? Do they live and sleep in that same wagon? haven't they never thought of leading they're own rebellion? I could go on pointing out other inconsistencies but it would spill out most of the (alleged) plot.
On the bright side, the movie is well paced, directed and keeps interest almost all the way, only the ending is too long and wannabe deep. The acting isn't bad, although someone should've told Chris Evans to lighten up a little and Tilda Swinton to tone it down. They're respectively dead serious as Leonard Nimoy and hammy as William Shatner, and that again sheds light into why the movie doesn't work as a whole, it takes itself too seriously to be evocative, and it is too far fetched in it's own internal logic to feel potentially possible.
So all in all, it is a competently directed action movie that if it hadn't been taken too seriously would have gone through with no glory or pain. As it is, I'm afraid, too many people that didn't understand it assumed they were too dumb and must've missed something deep, including critics and some film festivals. There are no hidden depths or meta message in this movie, people, it is what it is. Don't be lured by the hype, and if you don't see the emperor's clothes don't play along saying that you do, that just makes us all look dumber.