This book was hilarious and fun to read. Scalzi is a genius storyteller.

I'm beginning to dislike the star-rating system, though. I would give this 3.5. Why no higher?
Halfway through the book I felt betrayed. I was expecting one thing and Scalzi turns the book around and gives me something else.
Is it still good? Absolutely, but I thought it would be better given the great start and thus felt completely underwhelmed.

It's like when you are reading a mystery and the author reveals the first possible solution. You expect him to reveal a few more and then completely surprise you with a new solution that is nonetheless perfectly consistent with the story and ultimately more satisfying. This is not that type of book: you get the first solution, and that's it. That's the answer. Just have to wrap up the story now.
Fortunately, the humor and characters manage to make it enjoyable throughout.

A more detailed review is up on my blog: strakul.blogspot.com/2012/06/book-review-redshirts-by-john-scalzi.html