This is how I heard of this movie: Quentin Tarantino gave an interview where he was asked to name his favourite films that have been made since 1992 - the year he himself became a director. He listed them off alphabetically, but did say that THIS was his hands-down favourite, a (Japanese, of course) film he wished he had made himself, and it's easy to see why.
I checked to see if it was on YouTube, and voilà!
So basically, it's a take on the Running Man story, but on an island where 44 9th graders have 3 days to kill each other off until only one survives, or else they all die. They are abducted and shipped off to the island with some rations and a different weapon per student, then it's basically everyone for themselves. After the initial shock of the situation, some dive right in while others try and trust their best friends, even though somewhere down the line they know that only one must survive (kinda like Survivor, I guess). Not a deep plot, but never boring, with lots of violence and Mexican-standoff-type situations. You're thrust right into the story from the get-go, and it's fascinating just to watch how they're going to conceivably kill off 43 students.
The outcome's a little too nice n' tidy, but a fun watch nonetheless.
There have also been whispers of a Hollywood remake - no surprise there.