This novel starts like a "future history" story, where cometary mining is economically viable but dangerous and "the United Economic Entities" rule the world - apart from China, which is ostracised because it still experiments with nano-technology. Soon after it becomes an Alien Artifact story, reminiscent of Rendezvous with Rama and Eon. Then it becomes a desperate stakes survival story, complete with internal strife as well as external threat. Finally it becomes an Alien Zoo story, with the newly arrived humans interacting with some of the many cultures already there when they arrive.
Such an ambitious work is almost guaranteed to be flawed and the main flaw is that the book is too short to contain so much; many things have to be compressed heavily or glossed over almost entirely in order to keep the book to a reasonable length for a single volume. The several political reversals that take place begin to seem repetative and slightly far-fetched when squashed in this way. The Alien Zoo segment seems too short, though obviously open to a sequel (of which there is no hint at the time of writing).
The book is, according to Reynolds himself, an attempt to have a story about multiple interacting space-faring cultures that answers rather than ignores Fermi's Paradox - in that he does not quite succeed, because he spends so much time addressing the problem that he has almost no time to tell the story about the interacting humans and aliens....
The above is somewhat negative but this novel is in fact a gripping story with believable, flawed characters and a combination of ideas that provide continual interest, paced so that it accelerates towards its conclusion (if not real resolution) almost as the Rockhopper does on its journey to an unexpected final resting place.