The notes and chords here are pretty traditional here, but the eighth notes on E and the slide from G to A (sometimes harmonized) gives this riff a propelling momentum.  I tried going from C to D some of the time but I think this riff is better sticking to the C-B move, which is more intense.

How do you make a generic chord progression like Am-C-D sound interesting?  By playing with the chord voicing and adding notes that don’t belong there.  This riff keeps a sense of ambiguity and mystery by emphasizing the B note, the 9th in the key of Am — the tension note.  It’s the open B string so it rings out loudly, even when the chord beneath is D.  Not necessarily an ear-grabbing riff by itself but it has enough color to it that adding melodies and other elements on top of this riff as the foundation should be fairly easy.