I)

  See B2 section below. Starts in Eb major, ends in E major.

  A vocal melody is interrupted by a A-G-G bassline, making it sound like
  A7 harmony, but this is a trick. As the bass continues alone we start to
  hear this as what it is: 2-1-1 in G major. The guitars come in with G
  chords to confirm.

V)

  The verses starts in G mixolydian, with bass as a pedal. You can see the
  pattern they're building in the progression:

    G  C/G
    G  F/G  C/G
    G  C/G  F/G  C/G
    G       C/G  F/G  C/G
    G

  A bit of the pattern is then repeated in Eb mixolydian:

    Eb           Db   Ab
    Eb

V2) (with vocals)
B1)

  A lot happens in these 4 chords. The Bb is the V of Eb (shifting from
  mixolydian to ionian). The Db teases that we're back in Eb mixo, but
  instead of leading to Ab, we get harmonic planing down to a C major. The
  melody still has Eb, giving it a jazzy sharp 9 sound, and makes the
  following F chord sound like it functions as the V of Bb. So really the
  C is the V/V of Bb.

    V           VIIb    V/V (of Bb) V
    Bb          Db/Ab   C           F

  A full resolution to Bb is skipped in favor of 2 thrilling modulations:

    I      I
    Db     Eb  (We get a couple nice pentatonic lines here)

B2)

  We start in Eb major, slipping in a borrowed iv chord:

    I      iv          I
    Eb     Abm/Cb /Ab  Eb/Bb 

  The borrowed Abm is used to modulate to Gb major:

    ii   V        IV         V         V7      I
    Abm7 Dbadd9   Cbadd9/Eb  Db        Db7/Cb  Gb/Bb

  A i (Gbm) is used to modulate to E major:

    ii        I        ii   I  V7          I  iv       I
    Gbm/A     E/G#     E/F# E  B7sus/E     E  Am6/E    E

End)

  The G#m chords are dotted with brief A chords then we resolve to E:

    iii            V  I
    G#m7   A  x4   B  E

    v/II    II
    C#m7    F#7add11