"Redshirts" is founded on a fairly clever conceit. Anyone even vaguely familiar with the original "Star Trek" television series is surely aware of the disposable crew members who were slaughtered in sordid ways when the Enterprise visited strange, new worlds. They were frequently ranked "ensign" and clad in red shirts. In each episode, the viewer could reliably predict the fate of the "away team" members, often by shirt color alone. Scalzi affectionately lampoons this and various other conventions of the sci-fi television series.
In his novel, new crew members aboard the Universal Union flagship Intrepid recognize some alarming patterns, not the least of which is that those of their ilk don't tend to live long... or prosper (sorry!). They slowly discern that there's a "Narrative" dictating the outcomes of their missions. While the more senior crew members have adapted by avoiding recognition and staying off the proverbial radar, the new crew members decide to challenge the "Narrative".
While Star Trek provides fertile ground for this type of satirical treatment, there really isn't enough substance for a novel. The primary narrative of "Redshirts" is only 231 pages, but that's at least a third longer than necessary given the story. The plotting is uncomplicated and straightforward despite the metafictional elements which Scalzi, to his credit, took a bit farther than expected. Characterization, another good potential use of space, was nonexistent. This wasn't a clever metaphor on Scalzi's part (i.e., symbolic that "redshirts" aren't fully-fleshed out characters in the series) but because, rightly or wrongly, he chose to focus on the ideas underpinning the story instead of character-building. Additionally, the dialog was largely stilted and awkward, blatantly contrived to demonstrate Scalzi's sardonic, snarky wit. Practically every conversation was a succession of setups and one-liners. Admittedly, they could be funny, but the overall affect was ruined by the unnatural delivery. It was also distracting that each quotation ended with "he/she/[name] said". I tried to discern some clever motive for this but couldn't escape the conclusion it simply resulted from laziness.
After the overly long principle story is finished, three codas follow. They're short stories told in first, second, and third-person respectively concerning minor characters from "Redshirts" proper. In these short stories, Scalzi chooses to deal with some heavier themes. In fact, there are several powerfully written and affecting passages.
The first coda is similar in tone to the standard narrative. It takes a shotgun approach to humor and tries way too hard. It's occasionally funny, but the effort's too transparent. And, although it can be easily overlooked, the story doesn't logically flow from the earlier narrative. That said, it does provocatively assert the need for artistic integrity.
The final two codas are much more successful, the last near flawless. Given the light and jocular nature of the rest of the work, the emotional punch these stories deliver is all the more jarring. Eschewing humor entirely, the tone is much more serious as Scalzi considers life and its choices and obligations. In the final 26 pages of the book, he suddenly and unexpectedly humanizes the story, concluding the book on an exceptionally high note. While Scalzi deserves considerable credit for the final two codas, one can't ignore that the bulk of the work, though clever and moderately amusing, was mostly mediocre.