A fantastic premise, largely well executed. In the future, when people reach 75 they are given the choice to go into space and join the army, so to speak. Their understanding is that they will be "made young again" so they can fight,l and this is more or less what happens. It could be run as a hard sci-fi story, focusing on the tech and the war and the aliens. Instead, Scalzi takes it in a more human direction. The focus is on our main character's experiences, his thoughts, and most of all, his relationships past and present. I love the sort of resigned way he talks about his wife who died years before - stoical on the surface, but so painful underneath. He makes friends during training and they become his second family, and the way he interacts with them, the way he talks about those who die, is again, both detached and poigniant, as I'd expect from someone who's already gone through 75 years of humanity and loss and has tried to resign himself to it.Where this book lost me a little was the Marty-Stu-esque nature of our main character. He's good at everything. He makes the right decisions. Everything works out largely as he wants. It undercut some fo the peril of the story's climax.Speaking of the climax, the ending also felt a little rushed. Not the wrapup, but the conclusion of the climax. All in all, its a lovely book and I definitely recommend it.