Back before the dire imitators, genuinely superb horror films used to be made - horror films that represented the nation's feelings. One of the best examples is "Night of the Living Dead" and the Civil Rights movement metaphors.
Adam Simon's documentary is amazing in the fact that it manages to interview some of the greatest horror directors (George A. Romero, John Landis, Tom Savini, Wes Craven, David Cronenberg, et al) and examine what their films REALLY meant.
Admittedly I'm not a huge fan of the horror genre, but I love the horror masterpieces. This documentary covers every film I can imagine that represents greatness - it's definitely worth a look, especially if you're a fan of the films it encompasses (check out IMDb's references page for more info).