I think if you were inclined to go see it, you probably already know what is in store. I figure if the guy who made the Godfather and then won the Palme D'or twice sets 100 million of his own dollars on fire to make a movie you go see it.
Is it an overstuffed mess? Yes, but you already knew that. It's a movie made by one of the most successful directors of all time at the end of his life and he's clearly trying to use his medium to say something important to him about life, love, art, and society.
The wikipedia article is kind of a rollercoaster ride on its own. There's a list of the film's "literary influences" in the preproduction section and many of them are non-fiction: https://en.wikipedia.org/wiki/Megalopolis_%28film%29?wprov=sfla1
At times it feels like there was no script at all, and every once in a while one of the characters pulls a line directly out of Bartlett's Familiar Quotations or whatever Coppola was reading that week that felt important. At times it feels like the most expensive home movie of all time. There are certainly visuals where it is clear that an enormous amount of money was spent to get them.
There's definitely a MESSAGE, but I might need to see it again before I can tell you that the message is any more sophisticated than fascism is bad and repetitive and always has been, and life without beauty is crap, and there's always hope for the next generation.
It's about everything, and it's a pile of metaphors, allegory, and allusion to politics modern and historical. It's a crackpot movie.
But I don't know that it's a bad movie.
I'd advise you to take a friend, because it's definitely one to discuss over pie and coffee afterwards. Maybe it's a movie that you have to watch with someone else for it to hit right. Maybe that's the message, that we all need each other for anything to make sense?
Well, Black Canary missed it.