This isn't so much a book as it is an epic undertaking, both to read and certainly to have written. This is hard science fiction at its most pure: everything from terraforming to human anatomy to politics is based soundly in real science, and, as is true with all good science fiction, it is nearly impossible to tell the difference between Robinson's ideas and ideas he may have consulted with other scientists on. It's an incredible piece of work, while simultaneously being profoundly odd.
2312 takes place all over the solar system, but mostly on Mercury, Earth, and Venus. We follow two main characters, Swan and Wahram, and two supporting characters, Kiran and Inspector Genette. The driving force behind the plot is that there is something going on with the qubes, quantum computers that have largely taken over all the technical aspects of life. People have died, and the Inspector and Wahram, along with others in their group, are trying to find out why. Interlaced with this plot (which is vastly more complex than my own summary) are lists and extracts. These help to explain the science behind the changes Robinson has selected for this future, but also serve as a major distraction to the reader. I understand their use, and many of them are interesting, but they fracture the novel in such as way as to make this a seriously difficult read. Any reader who's main focus is plot will lose interest fairly early on, as one must persevere through some truly challenging and bizarre ideas. An argument can absolutely be made that this is what books, and science fiction in particular, are supposed to do, but the average sci fi reader will probably not make it through the entire novel. And this is a shame, as it really is a fascinating look into the future of humanity, and it's clear that Robinson worked extremely hard on it.
EDIT: I just got back from an event featuring Robinson and this work, and I have to say that I wish I had read the book after the event and not before. Robinson's reading of his novel showed that it is imbued with a certain sense of humor that I had only caught tiny glimpses of while reading. As I myself had concluded, and as Robinson confirmed, it is, at heart, a love story, and this lightens the feel of the book dramatically. Knowing these things now, I would have read 2312 as less of an undertaking, though it is still highly detailed and intellectual (and Robinson proved to be one of the smartest people I've heard speak).