There isn't actually much of a plot synopsis you can give to the film without spoiling it, so I'll stick to the setup a explained in the first 15-20 minutes. A group of college students are heading up to a Cabin by a lake in the middle of nowhere for a weekend. Unbeknownst to them, the Cabin is under full surveillance from some sort of organisation that is luring such groups up to it to be killed in gruesome ways, for some greater purpose. Its quickly becomes clear that the students are being manipulated into behavior that apes the sort of activities you see in more conventional horror movies, and as you'd expect, horror starts to unfold.
I'm pretty sure I missed some of the references and commentary in Cabin in the Woods. There are a lot of obvious homages - The Evil Dead, The Wicker Man, Texas Chainsaw Massacre, Hellraiser - and some bits that are homages to something I didn't get. There are quick-fire sight gags, a few scenes near the end that demand freeze-framing to spot everything, but actually, it doesn't matter. You know the story of what happens to college kids in an isolation cabin, the film knows you know, and goes about deconstructing it with wit and verve. I laughed as much as I winced, and I winced a lot.
It also serves as a critique of the genre as it stands; pointing fingers both at filmmakers and audiences by establishing the "victims" as likeable, fully formed characters that are made to act stupidly and suffer for our enjoyment. I'm guilty of confirmation bias here, of course, as from my position as a tourist into the genre that is one my main frustrations with it, but if Cabin in the Woods proves anything its that you can be pretty horrific and have smart, well drawn characters as well. Sure, there are some holes in the setup, but the central metaphor is strong and the pacing of the film (a brisk 95 minutes) stop you thinking about it till well after the blood stops flowing.
So, you don't have to be a horror fan to enjoy this film; Z, who is less of a Horror fan than I was, was gripped throughout, and spent a lot of time talking through it, just out of sheer nerves. It does get pretty full-on towards the end, so if you're really adverse to that sort of thing, be warned, but the film earns it in the build up, and the finale itself is satisfying and different. Sure, it's knowing, and fond of it's own cleverness, but it gets away with it skillfully, making it a fun and rewarding watch.