There has humor but also battles. But also of the human aliens. It is believed to be in an interstellar epic to colonize planets, and suddenly the most fundamental one returns to human emotions, we could have gotten in a general literature book (why I understood: if I 'I read the criticism of Kallisthène, J. Sclalzi comes from the general literature, this probably explains this) or at a Orson Scott Card.
History
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John Perry lives on Earth. He is 75 years old, is a widower, with little ties with his only son. He decided like many he seems to join the army. Less boredom by fancy a rejuvenated body. Indeed, the CDF (the entity representing humans in space) is recruiting men from ... 75 years. Why 75 and not 70 or 60? It is never explained, I guess statistically this is an age where there are still many men and women live, but enough désepérés by the degradation of their bodies to be likely to engage in the army.
It starts a bit part in "Space Cowboys." Smaller than 75 years old, did not know, and not knowing what will happen to them (everything is confidential), are in the same boat. They hope to have their bodies rejuvenated, because do not see why the CDF would bedridden soldiers. It's very funny and there is enough suspense and inventiveness to not see the time passing.
The second part, fighting, much annoyed me. Almost as if I were reading the pages of a book actually. Fortunately it is quite short. I do not reject that part was necessary to explain the evolution of the characters and the rest of the story. And maybe that male readers will appreciate this game with battles against aliens. Me this is not my thing (why not movies for special effects, but the book I have great difficulty).
The last part is the one I most appreciated. I did not see it coming, and I appreciated the subtlety of relationships that are built then. The conclusion is beautiful and satisfying.
What I think
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This is a book to be recommended to all fans of SF, which is both fairly succinct, quite successful and mainstream enough to be put in the hands of other players (just they arm themselves some patience maybe with the second part).
This is not the anticipation, it is not the space opera, in fact it is a bit all this and especially a great story about two human, one who dies in the first pages of the book. I feel that the book was not adopted in the cinema, which is a bit surprising. Certainly StarShip Troopers speak some of the same subjects (especially in Part 2 in my memories), but remains in the spectacular.
My only reluctance: the CDF is supposed represented all human if I understand ... but all humans crossed from the United States !!! Even the US-centered SF, or so I missed an important hint. This is all the more surprising that the author evokes Japan, France, the United Nations on Earth.