The premise of the book is kind of a postmodern twist. The film, The Last Days of Disco, is to be "novelized" and the publisher contracts one of the characters of said film (Jimmy "The Dancing Adman" Steinway) to write the novelization. Rather than do a straight novelization, though, Jimmy meanders and explores and expands on what the film shows. He also comments on how accurately the actors and directors present the material.
Some of the dialogue of the film is found in the book verbatim, some is embellished or truncated. All the characters are more fully fleshed out from the way they were depicted onscreen, and you wind up liking the "awful" ones a bit more and the "nice" ones a bit less.
The dialogue, naturally, sparkles and snaps and breathes. Not only the choice of words, but the ideas the characters present especially when they are counter-countercultural. Whitman has often said his films and books are his way of winning arguments he was too timid to engage in, and this shows it in spades.
The only potential drawback to this is if you have trouble deciphering if a written character is being deadpan-funny or serious. If you're so hampered, skip it. If not, it is clever and funny and a teeny bit poignant.
* The last person to publicly take me up on my suggestion was the lovely and gracious Gina, and she promptly vanished into thin air.