When reviews for 'Serenity' began dropping online, there was one common thread across every headline. Every single one exclaimed the ridiculousness of the films "twist ending". While I agree the film is ridiculous on the whole, it is consistently so and doesn't suddenly become the film it is at the end. The film telegraphs its reality so overtly from the [near] beginning, that you can't even call it foreshadowing anymore. To put it simply, there is no actual twist.
So what is a twist ending anyway?
I guess if I want to make claims about twist endings, I should start by at least broadly defining terms. There are generally two types of twist or surprise endings.
The first type is a narrative technique in which a reveal forces you to re-contextualize everything that came before that moment. Good examples of this type of twist are films like The Sixth Sense and Fight Club. When the reveal happens, it forces you to rethink every scene and conversation throughout the film and reevaluate the dynamics at play in each.
The second type of twist, is a much cheaper narrative technique where a reveal changes the expected outcome of the film and only changes how the plot could develop onward. The examples here would be any thriller or horror film where the killer/creature/thing miraculously survives or escapes after the narrative convinces us it was defeated.
So how do these general definitions factor into the plot of 'Serenity'? Obviously, we'll have to jump into MAJOR SPOILERS to find out.
So what did the trailer sell us?
The 'Serenity' trailer mostly sells it self as a straight forward thriller in which a woman tries to pay a man to murder her husband. Along the way though, it also sprinkles in an air of mysterying and confusion as to what's really going on around the island the story takes place on.
So what's the elevator pitch for the real story?
Savant child builds an incredibly elaborate video game simulation of his dad as a fisherman in attempts to escape the reality of listening to his mother's abuse by her new husband. The child's programming skills are so stupendous that the father character becomes aware of both the simulation AND the reality outside the game world.
But isn't that a twist?
NO! IT ISN'T!
It's essentially just really clumsy world-building. The story is revealed throughout the course of the film, but it never pretends to be one thing while secretly being another. From the very start, there is something wrong with the world we're playing in. Our protagonist is hunting an implausibly large tuna, he loses his catch for seemingly no reason, he's preforming 'fetch-quests' to pay for his routine activities, he's receiving context clues for his quests from his environment, he's experiencing bouts of missing time which usually correspond to the day/night cycle of his "level", and he keeps getting audio-visual hallucinations that involve some child seemingly outside of his active experience. And all of this is before it starts to get weird...
Very early on in the film we get a sarcastic comment about drinking alcohol out of a "Wolds Greatest Dad" mug -- clueing us into the fact that our hallucinations are a child who's not currently in the picture -- and then we're immediately introduced to the ex-wife who explicitly mentions the child. It's at this time we first see the child, through his laptop monitor, as he's furiously coding "something" at a speed that would make a Westworld technician feel inadequate.
It's at this point in the film that if you haven't arrived at the conclusion that our protagonist is inside some sort of computer simulation, your only excuse should be that you were too bored with everything so far to be paying attention.
So the ex-wife offers our protagonist ten million dollars to take her husband out fishing and then murder him. While their out on said fishing trip, we're given a recounting of a weird thing the husband had heard the protagonist's son say to him once. It was something to the effect of, "if i wasn't on my computer all day, I'd be thinking up a way to kill you".
It's at this point in the film that you no longer even have the benefit of boredom as an excuse. The child is programming a whole world to escape into, he wants to kill his stepdad, and the stepdad has suddenly appeared on this mysterious island where his mom is trying to pay the protagonist to kill him. The audience now has everything they need to solve the mystery. The remainder of the film is just opportunities for world-building or attempts at clever ways to use the premise we're operating under.
From here on out, we don't actually get any plot altering information. We just get the protagonist's realization of what we already know as the audience and characters dropping exposition to explain how the rules of the universe work -- including a character stating, "I am the rules".
In the end, the journeys and reveals of 'Serenity' aren't -- or shouldn't be -- a big surprise. They're just context clues to help you figure out whether the protagonist is in purgatory, experiencing some super natural test of morals, or living within a simulation of some sort. They don't change the trajectory of the plot, they don't make you re-contextualize any earlier scenes in the film, and they definitely don't lead to a twist or surprise ending.