As I am sure others pointed out as well, Redshirts reminded me a lot of Galaxy Quest. This story is a parody on Star Trek in which the "extras" aka "Redshirts" realize that something strange is happening on their ship. The leaders of the ship never die no matter how ridiculous their injuries were, and newbie crew are killed off almost instantaneously. This leads to hypotheses regarding how to avoid death, and they work together to try to save themselves from their imminent fate.
I laughed aloud a lot of times during the book and I don't typically do when I read books. However, I just don't think I am personally interested in sci-fi comedy, and I am not a Star Trek fan, so I suppose Redshirts is lost on me.
I really liked the Codas at the end, especially the Third Coda. I thought it was brilliantly done, and kind of wished the whole book was more that way, except I realize that Redshirts is a comedy, not a drama, and that is just my personal preference.