By all rights, I should love Greg Bear's "Eon". I loved his "Tangents", and enjoyed "Blood Music" as well. The subject matter seems almost perfect for me as well. If you told me a book by Greg Bear was about humanity unlocking the secrets of space travel in the aftermath of nuclear holocaust, I'd certainly be interested. If you added hints of time travel and parallel worlds, I'd be hooked.
For whatever reason though, the book left me a bit cold. In trying to understand why, I've been imagining a good science fiction story as a stool with three legs:
* Mind: The ideas or conceits that make the world different from our own
* Heart: The characters that help us feel the weight of this imagined world
* Body: The situations which allow the characters to explore themselves and the world they inhabit
A book like "Footfall" by Niven and Pournelle doesn't necessarily have the deepest characters, and its ideas are not all that challenging. What makes it enjoyable is the pacing, the characters are always doing something that advances the story. This a book that runs.
A book like "Dr. Mirabilis" has very few new ideas, and sparse action. It lives or dies based on how fully the reader sympathises with the main character. This is a book that must be felt to be enjoyed.
"Eon" had stronger ideas than characters or situations. It lives based on the strength of its ideas. This is a book which must be considered to be enjoyed.
On balance, the characters and situations could have been stronger, but if you want a bushel of hard sci fi to mull over on a winter's night, you could do a lot worse.