I don't think anyone *really* knows how to classify the show. I mean, for the entire first act and about 90% of the second act it was actually just a play where the characters "happened" to be singing at a party. Until the VERY end when Christopher Walken's character just burst into song, a la musical theatre.
It's definitely a shame the music wasn't preserved, though. I was young when I saw it and only remember bits and pieces of it, but I really enjoyed it at the time. I'm sure I'd appreciate it more today.
"You! You are the worst thing to happen to musical theatre since Andrew Lloyd Webber! And you, well, I just plain don't like you."
~Stewart Gilligan Griffin