In a genre full of environmental warnings, Robinson's gift is a vision that uses the environment and its complexity as the focus of all that happens, rather than merely as grim set dressing or allegorical overlay. And that vision is optimistic about what could, with sufficient will, be brought about. He sees creating utopias as a technical challenge to his craft — they're hard to do convincingly and interestingly. But he also sees them as an empty ecological niche in the imagination; if only to maximise cultural biodiversity, he wants that niche filled.
It's a good short introduction to Kim Stanley Robinson and his books.
I think I will have to reread the Mars-books soon.