I fought this book. There is really no better way to put it. It is a difficult read, but not because of its depth or complexity (which it has in spades), but because of poor execution. Bear overreached, and failed.
Greg Bear has written some wonderful books- Treason, Moving Mars, Forge of God, Eon, Blood Music. He is best at "action sci-fi", but some of his earlier works like Treason and Blood Music are also moving and lyrical. He must have grown tired of producing good, but relatively simple books.
In City at the End of Time, he spans trillions of years, creates entire sciences and languages, and tries really, really hard to put it all together. But the end result winds up being unreadable. Bear sets the mood, but is incapable of creating the necessary imagery and narrative to place you into the story. You spend most of the time just trying to figure out what the hell he is saying. Guess I will just go re-read Treason.