That song is all about texture. There's not a whole lot going on as far as notes, but he uses dynamics, timbre, and tone to move the song along. The bass with the weird effect (not sure what it is) kinda keeps the song going on the quiet sections, just creeping along. Then the guitar starts to fill in and help the bass out as the song picks up some energy, before finally the guitar goes to full on distorted power chords and the drums really kick it up a notch.

Really, that's why I like Alice in Chains so much. All of their songs had so much ambiance and there was so much attention given to the mood of the song as you move through it.