I really hope that you guys get out and see the movie this weekend. It's not because I want sequels - I'm not even sure they're possible - but because I want you to experience the movie under optimal conditions: in a theater packed with excited people who are discovering the mystery together.
Which means I'm giving you one last chance to back out before we get spoilery.
Turn back now!
You've been warned!
What's interesting about some reviews of the movie is that people don't quite understand who the heroes of the piece are. Here's a hint: they're introduced in the first scene. In some interviews Joss Whedon has said that the Richard Jenkins and Bradley Whitford characters are essentially he and director Drew Goddard. They're the guys behind the scenes, pulling the levers. At first they seem like they're probably bad guys, but as the film goes on and you understand what it is that they're doing you realize that they're the heroes.
Thats' the real twist of the movie. After all, you know right from the start that the events in the cabin are being controlled. But the assumption is that this is something insidious, something evil. I've seen a lot of reviews that utterly misunderstand the truth about Downstairs. The truth is that these guys are saving the world. Once a year they engage in a sacrifice that saves the world. It's terrible, and you may have issues with how they go about it - especially the way they blow off steam partying and betting - but the reality is that there are dark forces that needed to be contained, and this is how it's done.
As a meta movie it's interesting that the bad stuff happens when the characters themselves get meta. When our Virgin and our Fool discover the secret beneath the cabin - when they confront the controllers - shit spirals right out of hand. In Breakfast of Champions Kilgore Trout is allowed to be free after he meets Kurt Vonnegut, but in The Cabin in the Woods everything is destroyed when the victims meet the controllers. It's a meta commentary on meta commentaries.
But more primally it's about the dark forces within us that are contained by our appetites for scary, bloody things on screen. Horror isn't just fun, The Cabin in the Woods says, it's actually important. It's what keeps our eldritch forces under control. We don't shoot up schools because of horror... it's because of horror we don't shoot up schools. That's the most extreme example, but the reality is that scary stories help us process the unpleasant things in our lives - like the ends of our lives.
So the end of The Cabin in the Woods isn't nihilistic. We shouldn't be cheering for Marty. His level of self-awareness has ruined the whole thing; the movie is ironically arguing for the visceral, basic, sort of stupid appeal of horror movies. While Goddard and Whedon are saying 'Yes, it's really fun to think about and pick these things apart,' they're also saying 'However these things should be FELT first and intellectualized a distant second.'
That, to me, is why The Cabin in the Woods isn't a deconstruction of the genre. It's not finding emptiness in horror, it's reminding us why it's so damn important. Why we can fuck with the formula, but sometimes we have to get back to the origins and just wallow in the horror. For me The Cabin in the Woods is a reset button, connecting me back to the little kid who couldn't get enough monsters and wasn't always worried about the sociological implications of them.