I have just finished reading two Greg Bear books: City at the End of Time, and Mariposa.
Mariposa is the better book; a tightly plotted political thriller. City at the End of Time is just awful: amorphous and bloated, it makes little sense, and the ending provides no satisfaction at all.
The books share a common trait, though; they are both inferior retreads of previous Bear works.
City at tne End of Time is very similar to the his alternate reality fantasy from the 80's about the young wizard. The second book, The Serpent Mage, is about a world whose foundations are fallling apart and need a new creation to be saved. City has basically the same plot, but with a ridiculous many-worlds pseudo-quantum physics underpinning. Just as in Serpent Mage, the fate of the world lies with "breeds" who have unusual and unexpected powers. The old gods in Serpent Mage have the names of the gods of earth, while in City they are called Typhon, Sangmer, et. al.
Mariposa reads like Queen of Angels, with similar plot devices and even some of the same characters.
The themes---about how technology, computers and medicine will unleash new and sometimes dangerous capabilities, are interesting, but Mariposa says nothing that wasn't said better in Queen of Angels.
Also, like Queen of Angels, Mariposa falls apart near the end with a completely unbelievable, operatic weaving together of the storylines in the book.
By itself, Mariposa is not bad. It's just so disappointing to find a talented and interesting writer with nothing new to say. He could have skipped this one and City and we'd all think the better of him.