Worth it for other reasons as well. I think the Mars books are among the best examples of sfnal world-building, combined with politics, that I know; without needing a detailed knowledge of Martian geography in advance (the maps supplied are adequate for me) I got a tremendous sense of the scale and size of the planet, of the vast enterprise of making it livable, not a new Earth, but a new Mars. And Robinson raises questions about the political management of the environment and the wider economy on the new planet which certainly have resonances for our own time and place.
Each of the books has a couple of iconic moments which linger in the memory, and in Red Mars these are the deaths of the two leaders of the first colonising expedition, rivals both for political command and for Maya Totovna: John Boone, murdered at the direction of Frank Chalmers, in the first chapter (though the rest of the book starts from the colonists' landing, decades before), and then at the end of the book Chalmers' own demise, swept away by an ice flow in the geological and political turbulence of 2061. It's a story of growing tension between those who live on and love the planet and the insensitivity and eventual violence of the Earth-based authorities who try to control them, told from the viewpoints of different individuals among the First Hundred settlers, with a build up to catastrophe at the end. (Other memorable moments: the debate between Sax Russell and Ann Clayborne which sets the political context for the next couple of books; Arkady's horrifying fate; and the fall of the great space elevator.)
Red Mars won the Nebula for 1993, beating Assemblers of Infinity by Kevin J. Anderson and Doug Beason, Hard Landing by Algis Budrys, Beggars in Spain by Nancy Kress and Nightside the Long Sun by Gene Wolfe, none of which I have read (though I did read the original Kress novella). It was beaten for the Hugo by Doomsday Book and A Fire Upon The Deep.
Green Mars probably works best of the three as a standalone novel. We start with Nirgal, a viewpoint character from the second generation, growing up with a group of colonists in hiding since the 2061 catastrophe, experiencing the planet's puberty as he experiences his own (the key scene of the opening section is where he and the slightly older Jackie make love in the open air, once the temperature and pressure are high enough that they can do so). The book is very much the story of an underground movement plotting revolution - the usual excitements of sleeping with the enemy and subsequent capture, allies from Earth (a Soros-type billionaire who gets involved), plotting and planning the political and ecological principles of the society they want to build, and then seizing the moment for change when it arrives: the key scene at the end is Maya's taking command of the rebels from Jackie at the moment of victory, though a key symbolic moment is the flooding of the city of Burroughs by saboteurs and the evacuation of its population, made possible by changes in the Martian atmosphere, leading to a procession of people walking out their bubble and into a new world, which is another striking image.
Green Mars was beaten for the Nebula by Greg Bear's Moving Mars (with which it shares some themes), but won the Hugo against Moving Mars, Beggars in Spain by Nancy Kress, Glory Season by David Brin, and Virtual Light by William Gibson. I've read the Gibson but not the Brin or the full version of the Kress.
Blue Mars is a series of explorations of what happened next, what happened elsewhere, to the characters of the first two volumes. We get excursions to Earth and to the rest of the Solar System, with a mention of interstellar colonisation; we get constitution-building, explorations of the new planet and the new society that Mars has become. But it is also about death. The two killer moments in the book are, first, after Nirgal has set up and started cultivating his own little garden crater, filling it with plants and wildlife, showing it off to his friends, the whole lovingly described enterprise is wiped out in a sandstorm. No human character is even injured in the incident, but it is still tremendously sad. Second, as part of his scientific hand-waving to allow the same cast to witness all the stages of Martian terraforming, Robinson has gifted his characters with longevity. But this starts to run out after a while, and the suriving members of the First Hundred begin to die, one by one; the crucial moment comes when Maya fails to recognise a photograph of her long-ago lover, Frank Chalmers - a scene told from her point of view and then again from the viewpoints of those around her. The book, which has had a lot of death in it, ends with a summoning of lost memories, a reunion of survivors, and a celebration of where they have got to; with mysteries still remaining - for instance, whatever happened to Hiroko?
Blue Mars beat Lois McMaster Bujold's Memory, Elizabeth Moon's Remnant Population, Robert J. Sawyer's Starplex and Bruce Sterling's Holy Fire for the Hugo. I loved the Bujold and have read the Sterling (though don't remember much about it), and have no inclination to try the other two. Rather surprisingly it didn't even make the Nebula shortlist; in some ways I find it the most Nebula-ish of the three, and Red Mars, which did win the Nebula and not the Hugo, seems to me actually the most Hugo-ish. But there you are.
This is not really a 2000 page novel spilt in three. I think the first two books, Red Mars and Green Mars, work well enough both as individual novels and considered as a unit; if Robinson had ended the story at that point it would have been perfectly satisfactory. Probably the best book of the three considered individually is the middle volume, Green Mars, which is not the traditional setup for trilogies. Looking back at what I have written here, I note also that Green Mars is the one book of the three where the most memorable passages are not about death but about life. But I think Blue Mars is a satisfying completion of the trilogy (especially if considered with the spinoff collection of short stories, The Martians).