Short review because it's late and I'm sleepy but if I don't do this now I'll forget to do it later:
Tarkin has a completely different tone from the other new canon books I've read to date. Several things set it apart, such as good writing (yay!), really good characterization (double yay!), and a cohesive plot that flows smoothly (frickin' triple yay!). While Luceno's prose occasionally slips into purple territory, his portrait of the Empire's first Grand Moff is a compelling one and he managed to capture that "This is Star Wars!" feeling that I didn't get from A New Dawn and Heir to the Jedi.
So thank you, Mr. Luceno. May you get more Star Wars book contracts in the future. If you want them. No pressure. ;)