Anvil of Stars also my favorite Greg Bear book. Nobody read my review of this book on Amazon, so perhaps this is a better place for it:
I've read hundreds of science fiction books where humans have military conflict with aliens (though not yet the Forge of God). In nearly all of them, there are World-War-II-Naval-like space battles with weapons/ships/shields at near parity. I have always thought this to be highly implausible, and I thought an interesting aspect of this book was to consider three possible battle situations in space:
1) Your ship encounters a ship at a vastly higher tech level. If they detect you before you detect them, you are dead. Period. Your only possibility to win such a battle is to detect them first and destroy them instantly - and your chances of being able to do that are slim.
2) Your ship encounters a ship at a vastly lower tech level. Using the logic above, all that matters is you being able to detect them before they detect you. The technologies of stealth, electronic counter measures, detection, etc. are therefore all extremely vital in order to never be defeated by aliens with a lower tech level.
3) There is a possibility that you encounter an enemy close enough to your own tech level that the battle could last more than a split second. It is only in these instances that all the other things often written in other science fiction stories might matter - amount and type of shielding, weapons systems, quality of personnel, etc. But such battles are very unlikely, because technological progress is so fast. Consider what it would be like for any of today's industrialized nations with a substantial military to combat the most powerful nation on earth from 200 years ago - there would be no contest at all. The universe has been around for billions of years, so the chance of two races encountering each other that are within a few hundred years of each others' technology level is very low.
The above logic also applies to planetary defense as well, though with even more emphasis on not being detected.
This is the only SF book I've read that envisions future military conflict this way, and for that I give the book 4 stars. In my mind, this clearly deserves a place among the top 10 science fiction books in the military SF genre.
However, I did not care for the characters and character development and dialog which occupied the sluggish first half of the book. It wasn't until they started exploring the killers home system that I had trouble putting the book down. I did enjoy the dialog about ethical considerations of what the human ship was going to do, and the aliens they joined forces with were an interesting twist to the story and well done.
Bottom Line - the key to this book for me was an exploration of military encounters in space that struck me as vastly more plausible than the typical SF novel. Rewrite the book to remove most of the first half - and it would have been 5 stars for me.