I just finished City at the End of Time by Greg Bear.

City at the End of Time is a little hard to categorize, within science fiction. Greg Bear is known as a hard science fiction writer, and there are hard science fiction elements in this book, but the way it deliberately avoids explaining in detail the things that happen, instead focusing on how it affects the characters, will bother some hard science fiction fans.

Whatever category it fits into, it's one of the most interesting, but difficult, science fiction books of the year for me. Interesting because of the new ideas, or at least new spins on old ideas, and the impressive scope of the book. Difficult because it not only has a lot of quasi-mystical unexplained events, but it starts with a splintered viewpoint that is slowly developed throughout the book. The relationships between the characters, when and where they are, and even what they are, is only very slowly revealed.

Like another of the best SF books of the year, Neal Stephenson's Anathem, it throws the reader in the deep end of the pool and doesn't wait for them to learn to swim before moving on. Also, like Anathem, (SPOILER ALERT), it involves alternate worlds and characters who can shift themselves between those alternates in order to manipulate events. Anathem does more to explain that ability, while in City it is taken for granted, an approach that applies to the rest of the book as well. Everything in Anathem is eventually explained, where things in City are left only partially discussed.