Somewhat different to Scalzi's other novels that I've read (Old Man's War and The Ghost Brigades), this one has more humour and less action. It's also a little more coherent and paced better, a pretty natural result of his writing improving, I guess.
It's your typical science fiction diplomatic/espionage thriller about averting an interstellar war using a sheep. The hero is a guy who has the job of giving bad news to aliens for Earth's State Department.
I can't say any more without spoiling the story, so instead I'll just advise everyone to go read it.