Go see it. I can't tell you anything about it, plotwise, that wouldn't spoil it. But take my word for it, and go see it.
It's written by Drew Goddard (Cloverfield) and Joss Whedon (Buffy, Angel, Firefly, Dr. Horrible's Sing-a-long Blog, Astonishing X-men, Runaways, and a good proportion of every pop culture artifact I've enjoyed over the last decade. And Dollhouse. But we don't talk about that one). And directed by Goddard. And it stars Amy Acker. And Kristen Connelly. And the guy from Thor. More importantly, it stars Bradley Wittford (West Wing) and Richard Jenkins (Six Feet Under). Go see it.
It's also been getting a lot of hyperbolic reviews. Its detractors say it's not as clever as it thinks it is, and that it failed to properly deal with the racism and misogyny of the horror genre. And its apologists say that it succeeded in making it so that no other horror movie can be made again. Both of these statements are extreme. It's a movie--it's under no obligation to save the world, and it's the end of anything; people said that Watchmen would be the end of superhero comics, but thirty years later, that has failed to be the case. It's just a movie, but it's a good movie, and it's smart and fun. And I can't tell you anything about the plot beyond the fact that there is a cabin in the woods. Go see it.