First of all - WHAT A GREAT MOVIE.  I saw it in the theater when it first came out, and was utterly floored.  It actually gave me nightmares, which I'm sure was the intention.  It's remained one of my favorite films since then; although I rarely watch it because of its intensity, I've always held it in very high regard.  The script, the direction, the acting, the production values - everyhing just magnificent.  (And I also have a soft spot for Giorgio Moroder's Super70's synth score.)