My favorite movie of all time - Fellini's 8 & 1/2 - was the best foreign film of 1963. A black and white visual masterpiece, it's in Italian (and some French, German, and English) with subtitles. It tells the story of Guido, a film director, and his difficulties making the movie he's currently working on. It has long been lauded as a masterwork.
So, of course, someone decided to add songs and adapt it into a Broadway show. And, of course, that stage musical had to be brought to the silver screen. Thus, Nine.
Here is Guido, working on another broad picture with his famous leading lady (an interesting reference to Fellini's frequently working with his wife, Giulietta Masina?). The press is hounding him, his last two films were "flops" and here he is trying to bring another grandiose concept to the screen. He's freaked out, stressed out, tired out, and just plain down and out. So he skips out of the press conference and drives to a spa to get away from it all. He calls his wife, but doesn't tell her where he is, and instead calls his mistress and invites her to come down to the spa. In the meantime, his producer has found him and brought the entire production office to town so they can finish the movie on time. Needless to say, this does not help Guido de-stress. Then his wife arrives.
All of this is very similar to 8 & 1/2, often line for line and shot for shot, but, as Bruce pointed out, it's not the same movie. There are differences in character realization and plot development. Some characters are not in the movie at all, others have been morphed into someone only similar. Some scenes never happen, some are condensed into other scenes, or only referred to briefly.
Nine moves a lot faster than 8 & 1/2, I kept noticing that throughout the movie. Part of it is the condensation and the whittling down of the cast to fewer characters. Of course, bursting into song is also the tried and true method of advancing the plot, encouraging major character development, and letting the audience into the characters' heads -- all of which helps explicate and expedite the story.
So, I mentioned that 8 & 1/2 is my favorite movie, right? I love the intricate layers upon layers of action going on. I love the dialog and the amazing hyperbole it contains. Most of all, I love the ending - you've built up to it all along, and when it comes it's like the perfect bow on the present. Nine is like the other path diverging in the famous yellow wood - while Fellini & I take the one less traveled by, everyone else is on the one with a guard rail and signs. I didn't dislike the movie - there were some musical numbers I really liked, and some great shots - but I really felt like it was a watered-down version made for American audiences who are afraid of subtitles and just want everything spelled out for them. Bruce loved it, btw.