I enjoyed the book immensely, although it was a little short. It's practically Hugo-fodder if you know what the award tends to lean on---consider that
Starship Troopers,
Ender's Game and even
A Fire Upon The Deep were all about the perspective of unwitting citizen-soldiers in an alien war, it falls into the pattern.
The book was quick, reads like a screenplay, and was amusing although the science was a little thin. Scalzi's angle that most of the CDF's technology is stolen/adapted from aliens is pretty plausible imo, considering Vinge's
Technological Singularity expansion on Hurzweil's concepts: namely that technology becomes commoditized to the point where it becomes as culture-neutral as mathematics, and just as easy to steal.
I came in expecting much worse for a first novel actually, but I was pleasantly surprised. I did get the VERY strong impression that the novel started life as a script though, Scalzi does a lot of his development and exposition via dialogue and every resolution feels aggressive and physical enough to be on film or TV.