First things first, I do not like musicals. I've been pushed to see this by the infatuation over a lady. But trust me I was surprised to how much I liked it, even when I had negative expectations to it.
The film hands down is a wonderful homage to Federico Fellini, in his visual style, the women chosen represent Fellini's size of aesthetic view just like Kidman reminds you of young Anita Ekberg, Cotillard has the same diva material as Anouuk Aimee and Kate Hudson the figure and pallet of American stars that pleased Il Maestro Fellini. If you are familiar with this wonderful director, you'll enjoy "Nine" the better.
Then, I believe music helps to boost the theme and moral of the story. Generally outlined the whole musical is an ego-fest, all around Guido, Guido, Guido, his mess, his women, himself over himself. His ego being put into the light, with each song sprouting in the exact moment with "joie de vivre" and vitality, the women from Kidman to Dench showcasing enormous femininity and composure.
"Les Folies Bèrgere" piece says it clearly. What you need is the laughter, the lights, the color. The music, the "pleasure of living". Nine has it, it has it all while at the same time plays the keys that Maestro Fellini would have liked to hear if he was still with us.
