Lords of the Sith offers an excellent portrayal of the relationship between Darth Vader and Emperor Palpatine -- probably the best one I've read to date. As annoying as it was for Obi-Wan when Anakin was always a step or two ahead of him, Vader now has to deal with a master who is so many steps ahead that he's lapped him a couple of times. He's getting a tenfold taste of his own medicine. Add to that the fact that nearly everything Palpatine says to him has a double (or multiple) meaning(s), and it suddenly makes perfect sense why Sith apprentices eventually try to kill their masters.
If I was rating this book on characterization alone I would give it five stars. Who can make me sympathize with a serial killer, a lazy, indolent Moff, and a Dark Lord of the Sith? Paul S. Kemp can! But I'm not rating on characterization alone, and something else Kemp can do is drive me up the wall with his repetitive prose.
My brain seems to be wired to pick up on patterns. (I think most of us are wired that way, but my brain really latches on to them.) When words, phrases, and/or imagery is repeated, there's a good chance I'm going to pick up on it, which often leads to me being taken out of the story because I instantly think, "Didn't I just see that somewhere?" The following quotes are two of the best (worst?) examples:
They fired at buildings or aimed high, the red lines of their blasters writing lines in the mist.
Lines are writing lines? You don't say!
The sound of the V-wings streaking in sounded like a scream.
Sounds that sound like other sounds? Tell me more!
There was that single conversation in which one character's name was repeated sixteen times, and I can't tell you how many times Vader and the Emperor "fell deeper/deeply into the Force." Ships had a habit of going "over and past" other ships. And then there were the lines. Lots and lots of lines. I would have to skim back through to check, but I'd be surprised if a whole firefight went by in the book without weapons discharge being described as "lines," lightsaber blades included. Even that awesome interaction between Vader and Palpatine fell into a pattern, usually ending with Palpatine saying something seemingly innocuous and Vader pondering the possible meanings. It all started to feel a bit samey after a while.
TL;DR: Five stars for characterization, minus 1.5 stars for samey writing.