This riff starts out fairly straight forward, but as it transitions to the chorus it adds more and more twists, concluding with a really surprising chord.  That adding of interest keeps you engaged enough that when you go through it once you’re ready to hear it all over again.  The verse is essentially a predictable Em-G-A type thing, then it subtly transposes to the A tonality using the C-D progression, which is common to both Em and Am.  The F chord is the first surprise, then the second time the rhythmic twist adds more drama, and then finally the C-D section builds up to the C# chord that comes out of nowhere yet sounds like it belongs there, thanks to it being only a half-step away from the previous chord.  Don’t ask me how that chord can then lead back to the Em but it does work.  This is a tight verse-chorus pair and a fertile ground for a rocking melody.

This arpeggiated verse-chorus pair sounds like something that Phil Keaggy would write for his acoustic instrumental albums.  Fascinatingly, even though its tonal center sits in A minor this one sounds rather happy. It is using the Dorian harmony throughout (notice the D chord in there, using the note F# which doesn’t belong in the key of A minor) and that may have something to do with it.  It sounds simple but this one is a great practice for finger-picking — get all the notes to sound cleanly, keep a swinging groove, and make those harmonics pop out — not easy to do consistently.