Okay, but definitely the weakest of the trilogy. Felt more like a summary of how everything got resolved than its own story, and Will is increasingly hard to like. His heedlessness and sulking and self-absorption seem correct when he's thirteen; less understandable (or even believable) when he's in his late teens and chosen for special missions essential to the fate of all humanity.
As the characters grow older and interact with a wider range of the populace, the omission of women also becomes more glaring. Not only are no significant characters female, but there hardly even seem to be women in the towns they pass through. In the first book, a story of three boys escaping through the wilderness to freedom, it wasn't a big deal that they didn't meet or think about women, but when they're out recruiting dissidents -- and they explicitly don't recruit women, wtf is up with that?! -- it's a little unnatural. None of these young men ever think about girls? And the aliens are also sexist and only take male slaves while females get preserved as dead display specimens.
The alien-fighting plan was pretty dubious, too, I thought. But I guess it would be a crappy ending if the aliens won. Not that the ending was exactly upbeat. It's a sucky world, kids, and people are assholes! Don't get your hopes up too high. Enjoy some hunting and fishing while you have the chance, and avoid women and other aliens.