Kim Stanley Robinson does a masterful job of realizing a diverse array of characters, not the least of which is the planet itself. I found Ann and Frank exasperating, John and Nadia at times exhilirating and something of a disappointment, Sax and Hiroko equally inscrutable, and Maya making me wish someone would just slap her. I am astonished that anyone can keep track of so many personnae and keep their voices distinct.
Equally, I am astonished by Robinson's command of geology, meteorology, thermodynamics, and even economics. The details read well and ring true. For years, I wondered why no one had covered this sort of project in detail: terraformation, colonization, expansion. Most writers seem satisfied to take these things as read. Robinson shows what a great literary work a little delving (okay, a whole lot of delving) can produce.
On the down side, the details occasionally get in his way. In particular, I found three details more than a little discomfiting.
First, in the personna of Michel, Robinson outlines his personal psychometry of personalities. In doing so, he provides both an oversimplification of human character and an unwelcome glimpse at Robinson's methodology for building characters. Like sausage-making and legislation, perhaps this process would have been better left unexamined.
Second, I think the abundance of water in the substrate of Robinson's Mars is more than a tad optimistic. I realize that having to bring in water ice from the asteroid belt and Saturn's rings would have slowed the development quite a bit, but considering what a wealth of story Robinson typically finds in the details, I think this obstacle would have made for even more excellent writing opportunities.
Third, in a move that appears nothing more than a technique to allow character continuity, Robinson introduces the deus ex machina of a revolutionary new genetic longevity treatment. With no foreshadowing or side-plot leading to it, the main characters suddenly have a chance to live for a thousand years. My, how convenient. This device left he second guessing the author's motives through the rest of the series. I love the books, but I don't think this was a necessary addition. As the principal plotline of this first book readily demonstrates, key characters can die without compromising the story.