Much of what I have to say about Redshirts has been already said, and better, by other reviewers: the core of the novel is a fun, scifi-ish, meta-ish romp that is of decent quality, whereas the novel really comes into its own in the three codas, which are each beautiful and existential meditations.
I have only two complaints: Scalzi tags his conversations way too much ("she said") and it particularly bugs when listening to the audiobook. Wheaton, who is an exceptional narrator -- full of verve and hitting exactly the right cynical tone -- uses exactly the same cadence for every tag and it almost sounds rhythmic in this way that is very distracting. The second complaint is that the conceit of the books was well known a priori, and yet the majority of the book is spent leading the reader to it and describing it -- I would have rather spent more time with the characters -- and more fun, satirical romps through SciFiVerse.