It's a cliche to say that he used the wah-wah as an elctronic plunger, but it's not untrue either. Yet, there's more to it than that, becuase he wasn't using just the wah-wah to color his sound, he was using the electric sound of the horn as well, and he was using them in a quite unified way. And he was likewise integrating his playing into the group sound in a way that was indeed new.
One of Chick Corea's favorite lines about the late-60s/early 70s electric bands was that when Miles was playing, it was a beautifully focused music, but when he stopped, it often became a bunch of self-indulgent jamming. Regardless of how you feel abou that, I think the point that Miles could bring an entire group together by the power & specificity of his playing is obvious. But in this music, he got the group together on its own terms and then didn't so much "lead" them as he did give them further shape and definition by... "melting" inside/into them and their sound. Of course, it was his concept of the sound into which he was melting, but it was also a sound that was a lot more texturally complex and rhytmically entwined (again, if somebody can "do the math" on "Mtume", I'll be grateful) than any he'd made before, and yes, I do think it might have been the most, oraganically purest "original" music he ever made, although if you see a humorous irony bordering on the contradictory-yielding-the-truth between "organic" and "original", then we're probably thinking along the same lines...