I am a little tempted to let the trailer speak for itself. The vast majority of what is great about this movie is contained in this set up and concept. Stephen King came up with the idea when he was 19, and the youth of the cast and the premise show how a young man's mind can work when it gets a good idea. The close of the trailer "There's no finish line" is pretty great at setting up the sense of dred a film like this calls for. But, in spite of the fact that it is a King story, and that there is an overall sense of doom, the movie is less a horror film than an existential mediation on friendship, with a lot of death thrown in.
Cooper Hoffman and David Jonsson are the leads. Hoffman, who was great in "Licorice Pizza", plays the outgoing avuncular young man who signs up for this brutal contest, with a hidden agenda. While he is friendly with everyone, he does keep his deepest thoughts to himself. Jonsson, who was the best thing about "Alien Romulus", is equally friendly, and more forthcoming about his motivations. As a much more surface level character at first, he reveals greater complexity the longer they are on the road. The friendship that grows between Ray and Peter is at the heart of the film. How much of our hidden selves are we willing to disclose to another human being, when they may very well be the last person we ever talk to?
There is a whole cadre of other character types, some heroic, some nefarious but all with a sense of desperation on them that may be off putting to some audiences. The other thing that may be a problem is that the film is a nearly two hour walk and talk. Literally ninety percent of the film is watching the kids walk down a road. You may not want the episodes of brutality that accompany each contestants fate, but it is a welcome change in perspective when they arrive.
Conversation, if it is interesting, can be a perfectly entertaining acceptable form of film making, although it is a rare audience that will be patient enough for a movie where people just talk. As these boys walk the long march of death, they argue, joke, bond, reminisce, and otherwise find ways of moving forward. The idea of sleepwalking is brushed by quickly, so there may be legitimate questions about how this long trek works. There are some times when it is clear that King is attempting some sort of allegory about totalitarian societies. These mostly go nowhere and the flashbacks to earlier events do not feel as organic as they might. 
Two performances that will draw your sympathy and deserve a bit of notice are from Ben Wang and Judy Greer. Wang plays Hank, one of the contestants. He is incredibly confident and cocky, but otherwise appealing enough to become part of the core group of walkers. His desperation near the end of his screen time is a thing that will provoke pain and pity. Greer plays Ray's Mother, the only parent we get to see since she lives in the state where the walk is taking place. Her two brief scenes connect the audience to the reality of the contest, much more than the other crowds or spectators that the walk draws.
Be forewarned that one of the most gruesome scenes in the film, involves a bodily function that is not normally engaged in while walking. The vividness of the moment and it's unpleasant outcome will turn your stomach more than the fascism theme that is presented by Mark Hamill as the Major, who oversees the event. The film is quite thoughtful, but it is not as deep and meaningful about the world it takes place in, rather it plows the field of friendship and sacrifice, which all of us can understand.
