The adults have become so disgusted with the lazy, disrespectful youth of Japan that they passed a new law to teach them a lesson: every year, a class is selected to fight to the death on a remote island. Battle Royale follows one class's descent into madness (the actors look like college kids).
The plot is remarkably similar to The Hunger Games (BR came out in 2000), but three major differences make the movie feel totally different: this movie's rated R, so there are frequent fountains of blood; the characters all know one another from school, so the acts of heroism and betrayal have far greater impact; and the movie constantly shifts focus to follow ten or so major characters, so you never really root for a particular hero. Exciting, and constantly surprising.
You can rent the movie for $4 at Amazon, or enjoy it via Netflix streaming