Nice updating of the stories I associate with Heinlein. Covers a lot of ground, planetwise and timewise; short, sharp scenes of action and longer stretches of fun, idea-based chatter. Lots of ideas; a smorgasbord for the reader who likes to chew on things later: facets of war, what makes us human, how to operate in the military, how long love lasts, and more. My favorite part was exploring the differences in the two types of soldiers in this story--the old and the young--and comparing them with the soldiers I know from other stories (usually in their 20s and 30s).
This is the second book by Scalzi I've read and the second time I couldn't keep straight all the people in the main group (7 folks). I'm not sure if that's because they are usually introduced as a group (here in a canteen scene) or because they are so much alike: clever, wise, learned, and true (the fat, stupid, and bigoted die first.) I do know that if I'd been reading a print book, I would have turned back to that intro chapter and set the characters firmer in my head. But I was reading the story in e-form, and not sure where in the pixels the intro was, so I just kept moving forward. In the end, it didn't matter because it's war and even some smart people die in war.
In Romancelandia, we would describe these folks, and especially the first-person narrator, John, as Mary Sues: people too good to be true and somewhat hard to ride along with because of that. Even the one time John has a crisis of conscience (after much repeated bloodshed) his boss says "right on time, you're fine" and he recovers within that scene. Looking back, I remember scenes in Heinlein stories that have that sense as well. I loved those bits as a middle-schooler--I wanted to be that kid who didn't realize he was a math genius and then somebody told him he was and he learned all of the calculuses in a few weeks. Now that I'm middle-aged, I know I'll never be that person; I've made too many messes and these people start clean and continue that way. I'm thinking I shouldn't re-read the Heinleins.