Kim Stanley Robinson's followup to the Hugo-winning Green Mars and the Nebula-winning Red Mars carries the full weight of nearly two centuries of future human history on its shoulders. Blue Mars is as richly detailed and believable as its predecessors, but with an extra heft of sentimentality not present in the first two books. All the old familiar faces are present (at least the ones still alive), and it is the continuing interplay between the remaining members of the First Hundred Martian colonists that sparks this series closer.
Mars is becoming increasingly blue, with its own oceans and canals. But the planet's future is still bitterly contested between the Reds, who want Mars to remain mostly as it was first found in the 21st century, and the Greens, who would remake the red planet into an approximation of Earth. The inhabitants of Mars aren't the only ones with a pointed interest in the matter: Earth is in extremely difficult straits, its overpopulation problem exacerbated by the now-ubiquitous longevity treaments and its infrastructure and habitable land mass greatly reduced by the flooding resulting from polar ice cap melt. Overburdened nations demand that the infant world government on Mars accept huge numbers of immigrants to relieve some of the "home" planet's pressures.
So it is that most of the remaining First Hundred, among them Nadia, Maya, Sax and Ann, find themselves pulled back into the thick of current affairs and politics. Out of hiding after the trials of 2061, these older but ageless elders of the two-world scene struggle to keep a transplanetary war from erupting while preserving as much as they can of the improved society they've helped to create on Mars. Sax Russell, in particular, is determined to bring the original Red, Ann Clayborne, to an understanding of the beauty of his terraforming efforts. It is around the skittish dance between Sax and Ann that the final events of the Mars trilogy play themselves out.
Perhaps of greater importance personally to the surviving First Hundred are the "quick declines" taking a toll on their number. Increasing memory loss, both long and short-term, seem to hold the key to the sudden deaths of these first ancients. It is Sax who throws himself into the task of discovering (or not) the magic cocktail that will give him and his oldest friends their minds and lives back, and allow them to at last enjoy the brave new world, indeed universe, that they have brought into being.
Blue Mars is by necessity time-compressed -- by the end of the book and series, the major players are more than 200 years old. Some immediacy is lost vis-a-vis large planetary and interplanetary events, but it is regained in the personal stories of the First Hundred and their biological and intellectual offspring. Most compelling are the chase-and-retreat played out by Ann and Sax over decades, and the younger Nirgal's search for meaning and contentment. Robinson's Mars books are destined for classic status among hard SF readers -- Blue Mars puts the perfect ending punctuation on a top-notch series.