The Gershwin’s brothers ‘S Wonderful is in verse-refrain form. Before the verse starts there is a little 4 measure intro at the beginning, then the verse starts at measure 5 and goes until measure 28. The verse has a simple four quarter note whole note melody. From there the refrain starts up and does a syncopated rhythm thing until the end of the piece. Like some others said, verse-refrain is typified by the refrain. The refrain is the most recognizable part. If you have seen the movie An American in Paris the version of ‘S Wonderful only comprises of the refrain. You can see that version, sung by Gene Kelly and Georges Guetary, here (don’t worry this link actually works!)
The harmonic structure of the refrain is actually more stable than verse. It includes a lot of tonic and dominant chords. The harmonic structure of the verse is unstable because very two measures the same melody is repeated except for it goes up a whole step. It creates this feeling of uncertainty…when is this sequence going to end?
The three chords from the verse I have chosen to analyze are the C#dim chord in the third beat of measure 31, the Bflat7 (add6) chord in measure 33, and the Edim chord in the third beat of measure 57. The C#dim chord elongates the C7 chord that comes before and after it; it also creates some nice dissonance. The Bflat7 chord adds more depth to just the regular old V chord. And the Edim chord near the end of the piece offers a surprising embellishment in between the ii chords that go straight to V and then eventually a I chord that ends the piece. In measure 47 Gershwin uses a Enatural5 chord thing...going from the chord symbols above the music it looks like the way they tried to harmonize that chord among the Eflat majorness of everything is by simply by saying that the chord is intended to be a Gmajor chord.