Wow, this scene is perfect quintessence of this ep. I remember how i watched it for the first time. Those words Dean repeat through the ep was so right and obvious - 'what's dead should stay dead' that i never see it coming - that he said it about himself! Silly me thought it was all about dead girl and her father... and then was that scene...
I think it was one of the best tv moments of all time. The way how they film it, the way how dialogue (actually monologue) was written and how the scene was acted. You just feel it - all tensions and emotions tearing Dean apart...