These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: The Cabin in the Woods
Acceptable Targets: Three of the monsters featured in the cubes are two Klansmen and a KKK Grand Wizard, who may or may not be demonic
Alternate Character Interpretation: Was Marty justified in letting the world burn or was he just a self-righteous moron who doomed the world because he wanted to "rock the boat"?
Cargo Ship: Marty challenges Jules to make out with a wall-mounted wolf head while playing "Truth or Dare." She gets really into it... leading to the creeped-out reactions of the rest of the cast.
Cliché Storm: Intentionally invoked. The ritual pretty much has to be a Cliché Storm for it to work properly.
Crosses the Line Twice: The whole movie, but in particular Curt jumping the ravine only to hit the barrier, and the moment the elevators all open unleashing all of the monsters. And then they open again and unleash even more monsters. And then Patience.
Crowning Music of Awesome: The use of REO Speedwagon's "Roll With the Changes" in the office party after Dana gets out of the lake.
"If you're tired of the same old story / oh turns some pages / I'll be here when you're ready / to roll with the changes"
Ensemble Darkhorse: Marty. As "the fool," he gets most of the funniest lines, is the only one who figures out the Controllers' game, and turns into the hero in the third act. It's somewhat awesome that the guy who's half-baked into Narnia is the only guy who's actually Genre Savvy.
"Kevin." Whoever he is, he exists as nothing more than a name on the whiteboard (and a brief mention in the novelization) but he has inspired a plethora of trope entries, Epileptic Trees, and Wild Mass Guessing, far more than any other character.
Right around the time the film was finally released Supernatural coincidentally wound up airing an episode with a similar scene of an evil unicorn impaling someone to death with its horn.
Moral Event Horizon: The Organization crosses this during the Ritual, setting up innocent people to die horribly (even if it is for a reason). Some also feel Marty and Dana effectively cross this by letting all of humanity die.
We only get to see many of the monsters in brief cameos. One of the most memorable is the evil unicorn.
Rooting for the Empire: Once you know why the kids must be sacrificed, is it out of the question to start rooting for the monsters?
Spiritual Licensee: Believe it or not, this makes for a pretty good adaptation of the SCP Foundation. The main bad guys are a nebulous organization of questionable morality which possesses an enormous catalogue of monsters and other dangerous supernatural items (in this case, horror movie baddies), which it keeps and controls so as to prevent an XK-Class end-of-the-world event. And when the heroes find out about the lengths they're willing to go to, they take one look and say "fuck it, better to let the world end." The similarities get even creepier. S. Andrew Swann's proposal for SCP-001 is that it's the people who are writing the website. In this world. And a very good case could be made that, in Cabin in the Woods, the Ancient Ones represent horror fans.
This was discussed on the site and declared it to be Containment Breach: The Movie — unrelated to Containment Breach, the actual(ly freaky) SCP video game.
Iceburg 7: Though I'd like to hope we wouldn't fail so badly. emissary666: The idea that an entire site devoted to the prevention of an XK-scenario was so incredibly unprepared for a containment breach was just so shocking to me; especially how easy it was to initiate a breach event when they only kept Keter-level monsters.
However, many other users have pointed out that the SCP Foundation wouldn't be so utterly incompetent as to install a big red "RELEASE ALL THE MONSTERS!" button.
Unless the big red button was an SCP itself that had breached containment?
They Wasted a Perfectly Good Plot: Some reviewers said they would much rather watch a movie all about the company organising the events than put any major focus on the events inside the cabin.
Some of the other monsters would have made even more spectacular movies. Who wouldn't want to see an evil unicorn terrorizing a bunch of kids? Given what the movie's actually about, though, this is quite fitting; the Controllers are shown to be tired of the "traditional" scenarios and desire something that goes outside the box, but the Ancient Ones want Strictly Formula, and the Controllers know their audience all too well. They're wasting perfectly good plots, and they know it.
What an Idiot: All of the evil monsters can be released with the press of a single Big Red Button. The Controllers are just asking for it!