First off, a reminder that Umberto Eco is an Italian author. (as I'm sure most of the commenters here are familiar with The Name of the Rose or Foucault's Pendulum in English)
Based on this (and a few other) reviews, I'm not entirely sure how this book is supposed to be different from Foucault's Pendulum.
It is completely different.
Think of Focault's pendulum as an intellectual and noble ancestor of Dan Brown's Da Vinci Code, better written, better researched and much more intellectually rewarding. The story is beautifully twined in extremely fascinating scenarios and the general topic was much more relevant when the book came out.
Numero zero, on the other hand, reads like some long form notes hastily out together to resemble a short novel. The book is fast, lacks action (as noted by the review) and in the end really seems unfinished or unproperly edited.
It certainly wasn't something you'd expect from someone like Professor Eco. Plus, the plot and the setting are completely out off time and focus on a period - the 90's, or the late Wild West of media control by Berlusconi and his accolades - that's obsessing Eco for some time, along with the fact that he's more comfortable writing about the mechanics of old media that he, on some level, misses dearly.
Italian expat, here. Maybe I can help (even if I haven't read it - yet: I have read the Italian reviews when it was published).
You are correct in mentioning that it is "not too different" from Focault's Pendulum. Let say that while F.P. was mostly about esoteric sects and the people who believe in supernatural, this one is more about conspiracy theories (Italian post-war history and politics are full of events that have never been explained in a satisfactory manner) and how media can use "information" no matter if it real or fabricated, to bargain for power.
The meta-themes about real and fake might be universally interesting, but I wonder if the book can really be enjoyed by readers that have not been living in Italy for at least two decades.
I am not Italian, and have never lived in Italy, and have enjoyed Numero Zero very much (and all other novels from U.E.) Of course, everyone's understanding is influenced by his/her own personal experiences, and I may have missed subtleties that an Italian resident would have interpreted in a different way. But nonetheless, I really liked the book.
Based on this (and a few other) reviews, I'm not entirely sure how this book is supposed to be different from Foucault's Pendulum.