I think he really knows how to develope characters very well, and he stays very consistant with the rules he makes for each of his story worlds. I just think he writes very good sci-fi in general. His ideas on space combat and nano-tech are awesome, and he tends to take it as far as he thinks the technology can go, unlike most authors who only create tech in their settings with a very limited scope.
Dont get me wrong.... I love the guy. You happen to be reading the first of two of my absolute favorites (hamilton books).