The book is full of describing some different fictional city (or is it? one passage suggests maybe that's not the case), often with a different theme or flavor of strangeness that might be a metaphor for something in our lives. Every so often it changes it up by having Marco Polo (who is telling the stories of these cities) have a conversation with Kublai Khan.
I don't know if I enjoyed it as much as everyone else did (going off the almost universal glowing critic and reader reviews). Part of that might have been because I kept assuming the story was leading to some big reveal or something bigger than the structure of '4 chapters each describing a fantastical city followed by 1 chapter of conversation between Marco Polo and Kublai Khan'. I wanted something that tied it all together and made me go 'Aha! That's clever!'.
I never got that. If it was just billed as like a bunch of short vignettes about fantastical cities and that's it (no conversations), I might have just enjoyed picking it up, flipping to a random city, reading it, and enjoying it that way. The conversations periodically kept misleading me into thinking it was more than that, and I ended up getting impatient with the city chapters, wanting to get to the conversations where I was hoping a little more of the real story got revealed.
I'm still somewhat hopeful there really is more to it and I just missed it, although reading some reader reviews didn't seem to suggest otherwise.
That being said, maybe check it out, and if you go into it without the expectation that there's a grand overarching story to it you might enjoy it more. And some of the city vignettes were quite interesting. Although there were more misses than hits for me amongst them.