The Cabin in the Woods -- cowritten by Whedon -- is a different beast entirely, however, because it's a one-off; you could definitely set a hundred other stories in the same universe, but you only need one, and the one we got is so well-executed... I'm taking it as read, by the way, that you've already seen The Cabin in the Woods. If not, well, go out and see it first.
Unless, of course, you're interested in reading about the movie without seeing it at all, in which case I'll summarize it for you: A bunch of college students drive to a secluded cabin in the woods to drink, have sex, and generally do stuff that college students do. Meanwhile, their activities are being monitored by a sinister shadow organization who seem to be manipulating them -- pumping pheromones into the cabin's ventilation system, and so on. Sooner or later, the kids wind up in the basement which is cluttered with really weird stuff -- a bizarre snowglobe, a puzzle ball, various weapons, porcelain masks, and a diary in which a young girl details the slow torture of her family by her pain-worshipping father.
It is the selection of the diary which sets off the horror in the movie: an attack on the cabin by redneck zombies. Meanwhile, in the control room, bureaucrats and office drones orchestrate the zombie attack and herd the kids into dangerous situations. Eventually, Dana is the only one left. The control room celebrates; it's a job well done! As Dana is tossed around and generally mistreated by the hulking undead, everyone kicks back has a drink and generally-- wait, did someone hear the phone ring? It's not the Red Phone, is it? Everybody quiet down. Turn that music off. Something's gone wrong.
...And that's where I stop the summary, because it's just too good to get into the final act of the movie, where all the important stuff takes place. I will say that it is wickedly confounding, very, very clever, and if it falls short of consistent brilliance, well, it is certainly better than Good Enough.
The Cabin in the Woods has been heralded by a lot of rabid fanboys as the best horror movie of our time. I don't think it quite deserves that much praise, though it's definitely the best riff I've ever seen on the genre as a whole. Horror is becoming an increasingly self-conscious genre, and the idea of playing with horror tropes as say, the Scream movies do, has become so commonplace that it's descending quickly into self-parody. The reason this movie succeeds so well, I think, is that the self-parody is in the service of a serious story taken seriously. And it certainly helps that Whedon has a wry, effortless humor that both complements and frequently defuses the horror.
This really is a film for diehards, which might be why the negative reviews have been so negative. This is a movie for the sort of people who analyze the details in horror movies and find the repeating themes. Scream pointed out to most people that slasher movies come with rules. It certainly seems that way, but there was no grand design involved; fact is that the elements of such movies simply congealed into rules. Happily, Whedon and director Drew Goddard know the tropes, and have a good sense of when to skewer them, and when to honor them. It's a trick they can probably only pull off once; Goddard went Nixon-White-House-Aid on IO9.com and refused to confirm or deny a sequel, but I don't see how you'd do one (or a prequel) that would please anybody. After my third viewing, I can see that it's uneven and has some pacing problems, but fixing those problems would mean compromising something else. The more I think about it, the more it seems that the imperfect movie we have is the best version of this story that we could hope for. That's a criticism that comes with the territory of genre parody.
What other points do I need to hit? Oh, the performers. The kids are all really great, but Whedon has always had a good eye for casting, and these are mostly actors he's worked with before. In my experience, that's a good sign. I'm also very pleased (as is everybody else, if you read the reviews) with Bradley Whitford and Richard Jenkins as the -- what would you call them, technicians? These are well-written, well-rounded characters (even the small ones) and they've found good performers to flesh them out. Then again, that's the other thing Joss Whedon is good at.
Anyway, my wife is calling me to bed, so in conclusion, here's the trailer.
Also, I agree with everybody on all the blogs that it should have been a tentacle, but all things considered, it's a small loss.