This is the first Greg Bear novel I've read. And the story he writes is a frightening one. The Earth is undergoing an alien invasion from "unseen" aliens, i.e., aliens who stay hidden and let machine proxies interface with humans. What the human race does to enounter the aliens and fight back comprises most of the book. The plot itself is engaging and interesting, even though there are a few points where the story plods a little.
One of the irritating things about this book is the number of minor characters that come and go without adding much to the story. I also have to disagree with a couple of reviewers about the level of sentimentality - I found the book at times to be overly maudlin. Yes, we are dealing with a very heavy subject, but the repetition of some themes or certain thoughts going through the characters heads was overdone. Finally, I had a problem with Bear's writing style. It felt like it was written by a college undergrad. There's very little style to speak of. There are a number of other Sci-Fi writers (Niven, Stephenson, Simmons) whose writing is really a pleasure to read.
But on the whole I would recommend this book, especially to fans of movies like "Independence Day", or "Day The Earth Stood Still". This is a thought provoking book that will certainly make you appreciate the planet more. And I do plan on reading the sequel, "Anvil of Stars" at some point.