To a certain - and large - degree, to appreciate Robert Johnson's guitar playing it is helpful if you also play the guitar and have tried to play it his style. I've tried, and I can tell you that it's near impossible to capture the way he plays with all the subtle nuisances. I'm a pretty good guitarist but I can't come close. And as for Robert's singing...well!
And don't start me on Leadbelly. He is fantastic!