This is a book that is very difficult to get into because it presents so many new concepts all at once: a dormant godlike computer virus on the edge of the galaxy; races of humanoids, tree-like beings who move along in motorized planter boxes, and doglike aliens who are sentient only in packs; and a new way of viewing the galaxy as having increasing layers of technological complexity based on distance from the center.
This is "hard" sci-fi at it's hardest (i.e., most difficult to ingest). Yet it is also one of those books that expands your mind as to what sci-fi can be.
Personally, I am more of a fan of "space opera" - a small set of basic characters, usually engaged in battle involving a bunch of ships, with maybe 1 or 2 "futuristic/sci-fi" twists thrown in (e.g., Old Man's War or Dauntless). This one threw so much at me at once that I was overwhelmed and almost put it down forever several times. However, I pressed on and now, a year and a half later, I still ponder some of the concepts covered in this book.
I only rated this 3 stars when I first finished it. Now that I think back on it, and the how it has affected me since, I've got to throw in an extra star.
This book is not for the faint-of-heart - it is not a "read by the poolside" or "read before bedtime" book. But the investment will be worth it down the road. (For the record, I am contemplating reading another of Vinge's books, but I don't think I've quite yet built up the mental stamina required.)