This novel offers a bit of context on why Grand Moff Tarkin is the way he is (well, was the way he was I guess).
It’s not a deep character study, nor does it offer anything beyond superficial insight into his very bad actions (i.e. the Tarkins tamed a wild planet through aggression, fear, and the strict rule of law, so that’s just how Wilhuff Tarkin rolled).
The oddly friendly dynamic between Tarkin, Darth Vader, and the Emperor is pretty compelling. I’d have enjoyed more interplay with this trio. Unfortunately, the book is mostly a detective story / chase between Tarkin and a band of proto-rebels in the early days of the Empire.