In Fig. 2, we have the exact same rhythm part, but the lead riff has been altered to accommodate D, which is the 7th tone in E minor. Listen to the changes again and hear how the addition of just one note makes the harmonies fuller, adding extra tensions over what we achieved in Fig. 1. Now you have a full Em7 chord for Im, a full Cmaj9 for VI, and over the A5 chord, you have a 7, a 9, and an 11.

Now, check out Fig. 3. Here, we have repeated I–V–VIm–IV, capped off by a turn of IIm-bVII–I in D major. The lead riff plays around with the 5, root, and 2 of the key in the first half of each measure, and the 5, root, and 3 in the second half. This provides plenty of notes to fill out the harmony on those changes.

The E in the first part of the riff combines with D5 to give us a Dsus2 chord. But pay attention to that A5 chord: D and F# tag-team to make it into a bright and colorful A6sus4. Then, it’s A and D’s turn to make ordinary B5 into a Bm7 chord, followed by F# and A from the riff to give us Gmaj9 instead of just G5. In the second-to-last-measure, E5 is converted to E7sus4 (which you can also think of as an Em11), courtesy of the notes A and D. And for one ear-bending moment before the final chord, C5 gets a facelift vis-à-vis the notes A and F#, sounding a very spacey Cmaj13(#11).