I just came across this article
It's a pretty good piece on the power of Son House.

Robert Johnson's been dubbed the King of the Delta Blues. And yeah, it's true that his slippery genius on guitar dealt the cards that blues stringslingers have been playing ever since, and that the hellhound that was on his trail is one of the music's indelible images, and that his recordings hold a simultaneous beauty and terror that few artists have been able to raise. One could argue that nobody rekindled the twined blaze of those emotions as brightly as Johnson until Kurt Cobain come along.

But to me, Johnson is more of the blues' flamboyant prince than its king. The king is a man who both inspired and outlived Johnson, whose rippling slide can be heard resonating in Johnson's quicksilver licks, but whose own style was an unstoppable rhythmic juggernaut, full of muting and popping and frailing. And whose songs went Johnson's devil's music one better by summoning angels and demons, and whose singing then gave vent to the sound of their apocalyptic battle for his soul. Today Johnson's voice, cranked in a darkened car traveling through the one-lane highways of the Delta at midnight, still induces the willies. (Muddy Waters recounted that he once saw Johnson and was so unnerved he fled the scene.) But the voice of the great Son House not only sounds as though it could split the earth asunder, it is also the sound of a soul utterly alone.....