I agree with Mister Tee's reaction. Snowpiercer isn't a great movie -- I wouldn't want to oversell it as a profound dystopian masterpiece or anything -- but it has a lot of interesting elements, and is mostly exciting. As far as summer movie-movies go, this one has provided me with the most pleasure. I'm honestly baffled that The Weinstein Co. didn't just go for the wide release with this thing -- it's got Captain America in the starring role and a recognizable supporting cast, and it's in a genre that's very popular right now. I wouldn't expect it to make Transformers money, but many people in my real life who would probably be really into this movie haven't even heard of it. Seems bizarre to recast this one as an arthouse curio.
As I said, the movie's ideas about class conflict aren't especially complicated, but I do think there is one grabber of an idea. The film argues that the only reason for the lower classes' existence on the train is to procreate, so that poor children can serve a vital purpose in keeping the monied classes alive. These children quickly become useless in that capacity, until they're old enough to procreate themselves, and continue the whole vicious cycle. And once you get beyond child bearing age, you literally serve no purpose, and so your health, well-being, and even life itself is of no importance. I think there's something that's unusually powerful about the way the film presents this idea -- it isn't just a portrait of the rich riding on the backs of the poor, but of those in power (not coincidentally, white people in power) encouraging an overpopulation of poor children that essentially exist simply to do their bidding. Not to graft specific allegories on to something fairly broad, but I think you can see a critique of policies implemented by the 1% in power on all kinds of subjects -- health care, education, reproductive rights -- in the film's story.
I also think this was a movie that really benefited from the fact that I hadn't even seen so much as a trailer for it beforehand. Which isn't to say that there were a ton of amazing plot revelations (though, compared to what passes for narrative in much of today's action cinema, this was practically Raymond Chandler). But the sheer visual reveals of the various cars in the train as our heroes get closer to the front struck me as very exciting. In an era when so much about movies gets spoiled beforehand, I loved being in the same position our protagonists were, having no idea what was beyond the next door, and finding the worlds created consistently inventive. I think my favorite set piece was the one with Allison Pill as the schoolteacher. This sequence was where the movie got the most Hunger Games-y (the Wilford history film feels like a direct quote from the movie shown before Jennier Lawrence volunteered as tribute), but I still enjoyed the satire of watching children being indoctrinated with a revisionist view of history that practically becomes a religious exercise. (I also loved the detail of Tilda Swinton having to be paraded through the classroom in chains without the children noticing -- as if these kids would even care.) And I certainly didn't expect this sequence to conclude the way it did, a great example of narrative driving the action rather than the other way around.
I think the movie definitely dips in the last reel. The plot just seemed to lurch to a halt once we got to the front car, for, as Mister Tee puts it, way too much talking. (I did get a nice laugh here, though, because I had no idea who was playing Wilford -- when that character finally appeared, I just thought, of course it's him!) I also felt like the ending wasn't quite as satisfying as I'd have wanted it to be. It's obviously ambiguous on purpose, but it struck me as more frustratingly vague than anything else, probably because it was given to two relatively minor characters, whom I didn't feel I knew all that much about. Not sure where I'd have wanted the movie to go, but I felt like I wanted at least one more story turn to leave me with something more than just ambiguous optimism.
But on the whole, I think it's a movie worth seeing. You'll certainly get more visceral pleasure out of it than most of what's playing at the multiplex right now.