Old Man’s War is Scalzi’s first published fiction novel, and it shows. It’s certainly enjoyable – it reads like the offspring of Cory Doctorow and Robert Heinlein – but it’s rather flawed.
It doesn’t help that it is most similar to my least favorite work of Heinlein’s: Starship Troopers. Very effective at making people never want to be associated with armed forces or warfare in any way. I suspect it would have the opposite effect on some people, in the same way that Heinlein’s did, but those people are beyond help anyway.
One fairly trivial problem is that Perry was diagnosed with testicular cancer during his physical exam. Given that he was seventy-five years old, that’s moderately unlikely. Testicular cancer is usually a young man’s disease, with 90% of cases occurring before the age of fifty-four and the majority before the thirties. It’s certainly not impossible to develop it in relative old age, but it’s sufficiently implausible that it brought me out of the story. It’s by far the most unlikely thing to have happened by that point in the novel, and it begins with a seventy-five-year-old man joining the army. In space.
A more serious one is that it simply doesn’t make sense that Earth survived long enough to produce a technological civilization in a universe filled with hostile, colonizing intelligences, many of which have a taste for our biochemistry and sufficient technology to make harvesting our flesh worthwhile resource-wise. (They certainly could grow flesh in vats, just as we can farm fish in tanks. Wild-caught food is still available, and is a status symbol for humans. Why should it be otherwise for aliens?)
I much prefer galactic civilization in The Android’s Dream (many interstellar civilizations, most of which have no interest in Earth) to that in Old Man’s War (many interstellar civilizations engaged in an endless war over living space and resources). Sadly, it seems mot of Scalzi’s work has been set in the OMW-verse. Oh well.
I’m not particularly fond of the ideological stances implicit in the work; they’re very common, though, so it’s not as if they’re surprising.