I absolutely loved this book. First of all, I love Scalzi's writing--I find him hilarious. And second of all, there is a huge emotional payoff as the story unfolds.
I also love Joe Hill's comment on the back of the book: "Redshirts is (a) ruin-your-underwear funny, (b) a mind-bender sure to Philip K. Dick you over, and (c) absurdly rich in ideas and feeling. John Scalzi sets his imagination to STUN and scores a direct hit. Read on and prosper." (Stephen King's son can be pretty funny himself).
Here's the basic premise of the story. Andrew Dahl is assigned to the Universal Union Capital Ship Intrepid. The year is 2456. He's thrilled to be assigned to the ship's xenobiology laboratory with the chance to serve on "Away Missions" alongside the starship's famous senior officers. But soon crew members start comparing notes and realize that every Away Mission involves some kind of lethal confrontation, the ship's Captain, Science Officer, and handsome Lieutenant always survive these confrontations, and at least one low-ranked crew member doesn't.
[This scenario should be immediately recognizable to any Star Trek fan. The title of the book comes from the color of the shirts of these expendable crew members whose only job was to be killed in a spectacular way (and Star Trek came up with some very creative ways for these crew members to die), so that Shatner, Nimoy, and Kelley would have a body to emote over, and the action/adventure element of the TV show would be furthered. ]
The savvier members of the Intrepid start avoiding Away Missions at all costs. Then Dahl stumbles on information that completely transforms his and his crew members understanding of what the starship Intrepid really is...and the craziness begins.
It is what Scalzi does with this craziness that is really interesting. This is where he uses his doctorate in psychology (that he received from the University of Chicago) and takes us into weird territory. I don't want to give anything away, so that you enjoy every delicious twist and turn of his narrative. But I must say that the three Codas at the end of the book made me cry. Really cry. No surprise there, as Scalzi said he cried when writing them.
Funny science fiction hasn't really been in vogue since The Hitchhiker's Guide to the Galaxy. Maybe the success of this book will let the powers that be know that there is a huge audience for it.