There's no way to talk about
The Cabin in the Woods without giving away some really relevant twists that had me and a friend alternating between giggling madly and joining in hushed conversations with our theatre neighbours. But it's a really, really good movie.
It's Joss Whedon, and it definitely has his signature all over it. It's self-aware and humorous, while genuinely pulling in "startle me" moments, great tropes, and all the fun things about horror movies. The direction is amazing, with a lot of recognizable angles and set-ups that are standard in American horror. Music and sound is well-played, with excellent use for background effect. The writing is superb.
And the characters...
Well, the characters are part of the twists. You can pretty much figure out the main storyline by the trailers, but the "how" and "why" is the important bits. And the fun. It's not just another slasher, despite a bloodbath near the end. It's very much Whedon's commentary on the state (then-- since this is a delayed release, and remembering movie trends for the past decade does help one of the throw-away jokes; but that sort of knowledge isn't necessary for enjoyment) of the horror industry. Yes, there are the standard archetypes of the genre, but it's... Well, manufactured.
The writing is brilliant, the direction is lovely, the story is absolutely entertaining, and it's just a fun film to see. Go with a friend, grab a popcorn or snack, and just enjoy it.
Whedon also likes to re-use as many actors as he can-- so you get Amy Acker, Tom Lenk, Jodelle Ferland... And a very GLADoS-esque few moments with Sigourney Weaver.