More like 3.5 stars for me.
Redshirts starts fairly strong, detailing the story of a bunch of new Ensigns on the starship Intrepid. It doesn't take long for them to notice that something is off on this ship, because Ensigns have an incredibly high fatality rate on Away Missions. They start to investigate and find out how this comes about, which in turn turns this book into probably the most meta book I have ever read. In fact, it turns so meta that everything after the explanation falls a bit flat for me.
However, the book is saved by the three codas at the end of the book, which are less satire and more serious. The last coda in particular was very touching.
The writing was enjoyable, and so I will have to check out more of Mr. Scalzi's work.