If you haven't seen that much Star Trek (original series), you might not recognize the red shirt plot device. Essentially, a red shirt character is designed to be cannon fodder. They're usually unnamed characters who get killed before the first commercial break for a bit of extra dramatic tension. In Scalzi's novel, the story is told from the perspective of these minor characters.
Shortly after being assigned to the Universal Union ship Intrepid, Andy Dahl realizes that there is something weird going on. Crew members go out of their way to avoid away missions, to the point of tracking the location of high ranking officers so that they can duck into closets or rush off on "urgent" errands. One of these officers has been shot, infected, and severely injured repeatedly, but still manages to be back on duty within a week or so. Physics and biology get impossibly bent to allow for things like time travel, lucky coincidences, and general bullshit. After a few weeks, Dahl meets Jenkins who has the bizarre theory that they are all in a bad science fiction show. Weirdly, it's the only theory that fits. And then the book gets really meta as Dahl and his friends, fellow cannon fodder, try to find the writers of the show to stop them from killing off crew members in ridiculous ways.
I loved reading this book. There are so many jokes about stock science fiction plots and characters that you'll be laughing every couple of pages. And on top of all that genre-bending stuff is a very poignant story. You might not think of this as the kind of book that invites deep analysis (other than to point out the flaws in bad science fiction), but it really is. Once the characters start to come to terms with the fact that they are fictional and real at the same time, they start to suffer from some very serious existential angst. If you know that you were created to die for a little dramatic tension, what's the point of carrying on? If you can't avoid your pathetic fate, why try to find a way out? I like to think that Camus would have enjoyed this book. (You know, if he wasn't fifty years dead.) By the time you hit the three amazing codas, this book gives you all kinds of dilemmas to ponder.
This book is simply amazing.