Even in 1985, when the Cold War was still very much within living memory and the way of life it had dictated something familiar to every thinking reader out there, this book must have had a terribly anachronistic feel to it. The technology is there, the potential is there, but none of the characters seem to have evolved past the primal Cold Warrior types. The Americans come across as paranoid and greedy to keep all the treasures for themselves ("The Libraries were a purely American preserve... by order of the President," as though the American president could have the power of actually enforcing such an edict short of threatening to blow up the libraries if an impure and non-American foot ever crossed their threshold...), the Russians seem to be straight out of the worst parodies of early James Bond, the Chinese are kind of tapping in place trying to figure out what their role in all this is, and the rest of the nationalities up there seem to have been tossed in to season the polyglot nationalist salad. Eon, twenty years after its initial publication, suffers from this hindsight, to the extent that it sometimes gets so annoying and in-the-way that it's hard to concentrate on the storyline.
Then again, Arthur C. Clarke wrote novels with the same clichéd geopolitics (2010, anyone?) and arguably similar problems with believable characters and no one finds that particular cause to trash his works, do they?
Eon's fundamentally a work concerned with opening and closing possibilities. The opening comes when a vehicle bearing a suspicious resemblance to the asteroid Juno emerges in a burst of gamma rays at the edge of the Solar System and decelerates into Earth orbit. The explorers (NATO, Soviet, Chinese) who arrive discover not only a generation starship but--quickly hushed up--evidence that it was not only populated by humans, but that its inhabitants disappeared down a mysterious space-time corridor extending beyond, somehow. On the Earth, possibilities are starting to close down thanks to an intensifying Cold War, one that already broke out into a minor nuclear war, is getting worse as the different parties fear that the advanced technology of the generation starship could change everything. And in the meantime, the generation starship's descendents, living down the Way in their artificial city, are starting to be distracted from their trade and their wars with other factions in other places of their bizarre universe by events at home.
Early Greg Bear may not have been a convincing writer, but he was certainly good at depicting vast impressive things. His generation starship impresses; his depiction of an Earth on the verge of catastrophe scares; his depiction of the Way and its cities and its connections awes. And, at the novel's end he provides readers with another way to check whether or not they're in an alternate history. I can't go into the details of the plot in much detail since Eon is rather spoiler-heavy, but I can say that the novel is ultimately concerned with the characters' efforts to find some sort of home, perhaps particularly brilliant Los Angeleno physicist Patricia Vasquez to find her home again.
So. Read Eon for Bear's grand scheme. Don't read Eon looking for especially convincing characters or moving writing (although there is that one passage--no, no spoilers).