(His Second Rhapsody has never had the fame of the 'Rhapsody in Blue' but is, to my mind, much more satisfying as a concert work.) Mr. While I agree that the 'Rhapsody in Blue' is not satisfactory as a 'classical' work, it's form is too diffuse and the composer didn't really know what he was doing at this time, I think he made up for it later on and then some. I don't recall his exact remarks but they are to the effect that all of Gershwin's serious music, consists merely of strung-together show-tunes.
It is interesting that Virgil Thomson's negative remarks are given at some length but these are expressions of envy in my opinion. A fine documentary both as a presentation of the composer's life as well as his music including many observations and opinions.