If contemplating the moral state of society doesn't sound interesting, this movie isn't for you.
This isn't one of those movies you can just jump into. You need a good grasp on historical Roman knowledge (i.e. read Sallust, Cicero, and Aurelius), have a taste for Art Deco science fiction themes (e.g. Metropolis), and an affinity for Avant Garde theatre (e.g. Eccentrism). Otherwise, most of this movie will go right over your head.
This movie really should be branded as a high-budget indie film, since Coppola basically had complete creative freedom in making this. Which is probably why so many people aren't liking the movie.
This is going to bomb at the box office, but will probably turn out to be a cult classic in the long term. It won't bomb because it's a bad movie. It'll bomb because people won't understand it. And I think Coppola already knew that.