Wow. Not one of Greg Bear's finest, I would say. Although the last third does try to make up for the plodding two thirds.
Like most sci-fi written in the past talking about "the future" that is now our past, it has a few stumbling blocks where he didn't get it quite right. Forge of God was written in 1986, the cold war was still on with no end in sight, computers were just starting to reveal their usefulness as personal computing platforms and modern data storage techniques were coming to light.
Set in 1996, he gets a surprising number of things right: personal computers small enough to carry around to hotels and airplanes, optical storage media as a standard, and flat-panel screens. On the other hand, there are a couple references to the Soviet Union and Marxists as adversaries to the U.S. that are kinda grimace-worthy.
True to Bear fashion, however, the akwardness of the future come and gone is pretty easily overlooked, as he focuses mainly on the people, not the tech, and the ways that their lives and character are changed over the course of the novel.
Basic premise: two alien "bogeys" are discovered on earth. The occupants of one, landed in Australia, say they bring enlightenment for all of humanity, and start teaching those who'll listen about advanced physics etc. The second craft, landed in Nevada, ejects a dying alien who lives long enough to claim that "the planet-eaters" have come to destroy Earth and there's nothing that anyone can do about it. (There's also a third, but we never really find out about it because the Evil Soviets are hiding it.)
So what happens? A group of scientists are wrapped up trying to figure out what's going on and who to believe, a group of government officials are trying to decide how much and what to tell the rest of the world and eventually the planet is destroyed in prose at times so moving and evocative that I don't recommend reading it alone in an empty apartment like I did. I put the book down and picked up my cat so I could hold in my arms a breathing, fuzzy reminder that the planet does in fact still exist.
So where does it go wrong? Well, there's a story line about a dying scientist, the point of which I'm still trying to understand. As a friend to one of the main, and most developed, characters, it could have been a great vessel for exploring the fragility of human life and the upcoming confrontation he'll have with his own mortality, but instead it just kinda peters out.
As I mentioned earlier, it starts out kinda plodding and slow. It falls victim to the Heroes Phenomenon - there are a lot of characters, we don't know why they're in the story and we're not terribly inclined to pay attention to them. Eventually, like Heroes, it does all come together and make sense, but I was left wondering if there isn't a better way to get there.
Also, like the last Harry Potter, I really could have done without the epilogue. The story itself sets up enough information as to what's going to happen "afterward" that we really don't need to be propelled a couple hundred years into the future to have it spelled out to us. Not to mention, it was probably the lamest part of the book.
I would say that his later works are definitely better than this, although I can see the promise here for those. I rate this book so high because of the end really the meat of the story. Perhaps it would have worked better as a short story, truncating the beginning and focusing in on the main events as they happened.