Basic outline: Earth has been destroyed by killer robot spaceships. The few remaining survivors send some of their children to avenge the planet. Supposedly there is another race called the Benafactors who, having built spaceships of their own to hunt down the robot killers, take the children (young adults, really) to hunt them down because it's the "LAW". I have to ask: What kind of beings make a Law that can only be understood poorly, if at all, since the Benafactors who sent out these Ships of the Law cannot be questioned directly (out of a sense of self preservation)? I give this book only 4 stars not because the book is bad (it's great) but because it's frustrating that the humans are obviously in over their heads in terms of carrying out a completely ALIEN system of justice that has no limits on time or distance. In other words they can travel for hundreds, if not thousands, of years across unimaginable distances (something the book conveys well) to find what? A civilization that has forgotten its horrible past and doesn't know enough to FEEL guilty let alone BE guilty. As the book lamely asks: what about redemption? It's not answered to my satisfaction. My biggest complaint is that the Benefactors don't seem to care that Earthlings (or perhaps any race they happen to save) don't have any idea what kind of moral/legal/social/galactic framework they are becoming involved in. Sure, it's great that they get these ships to go out and avenge Earth but who ARE the Benefactors? Why do they care about revenge and if they care so much why don't they just do it themslves instead of going to all the trouble of "training" the survivors and telling them only that it's for dear old earth? We don't get any other explanation 'cause the benafactor built robots who guide the children either can't or won't tell. Giving out info is apparently against the best interests of the race(s) that sent the Ships of the Law out in the first place since the ship might be captured by the machines they are trying to destroy. Implying that earthlings might turn into equally dangerous predators as the killer robots doesn't seem reason enough not to give out as much info as possible concerning WHAT you're doing, HOW you're doing it, WHOM you're doing it to, and WHY it must be done. Blind faith and desire for revenge can only go so far.
Anyway, I enjoyed the book despite these questions and recommend it. The science is engaging/realistic (more or less) and the characters are deep enough to be enjoyable. I do NOT see this book as derivative of Ender's Game at all. IMHO they are polar opposites. One is a revenge seeking space opera and the other is a quest for redemption. One last caveat: Both Ender's Game and AOS recognize that as humans we don't always have the option of forgiveness. Not right away, anyway.