The only blemishes on the book are, in my opinion, the ending and some of his treatment of the evolution of Earth and the war on Mars. For some reason, I did not find the ending section (told from Ann's and Nadia's viewpoints) nearly as compelling as the rest of the book. At one point (a plot spoiler), I thought Nadia seemed to act out of character, and Ann's section seemed . . . tepid, even though there was plenty of action, emotional and otherwise. I just didn't care as much as I had earlier. It may be a case of sequel syndrome, where the lack of a forced conclusion allows the author to peter out, rather than writing a strong ending. I don't know, but that was the only technical problem I found with the novel. My dispute with Robinson on the subject of Earth is much more open to contention; simply put, I am a skeptic about the imminence of overpopulation, which plays a great role in Robinson's Earth. I also disagree with some of the directions he takes geopolitics, but a geopolitics is hard to predict, so I'll leave it aside. Robinson's portrait of war on Mars is also not what I imagine war on Mars would like; in essence, even in an environment as hostile as Mars, I suspect that fighting a determined resistance movement would be well-nigh impossible. There also are a great number of nitty-gritty tactical details that I don't think he gets right, which I won't go into for sake of brevity.
In the end, RedMars is an outstanding book. I look forward to reading the rest of the series, and I hope it maintains the same quality.