For a Star Wars book there is very little Lightsaber duels or space battles but that is not the purpose of this book. Instead this is about political & corporate intrigue, corruption and subterfuge. 
 For a thousand years the Sith have worked in secret to fulfill "The Grand Plan" to collapse the corrupt Republic and misguided Jedi. 
 Now Darth Plagueis is ready to fulfill the plan but he has also been experimenting on extending life so he can rule forever. But in order to accomplish both he must break with tradition and work with his apprentice as partners, for they can only extend life of others, not themselves. He finds and mentors Palpatine, the man who will become the Emperor. It provides a unique narrative perspective, told from the dark side. 
 Star Wars fans who enjoy the lore will enjoy the many aspects it covers: Count Dooku decent, Darth Maul, the trade federation blockade, Sith roles, the Jedi, establishing the clone army and manages to show the Emperor's rise to power without domesticating (softening) him. It also Ret-con (fixes) or clarifies midichlorians as being more an indicator and not a cause of The Force. 
 The downside of this kind of book is a lot of the action is done behind the scenes. We often hear the results of a successful plan instead of witnessing the effects first hand. Also as mentioned very little Lightsaber or space combat, but they do exist. 
 Personally I have a fascination with grand plans and political intrigue so I enjoyed this book. 
 Technically it not part of the new Star Wars Canon, but Tarkin (which is) hints a lot at this book's events, so most of it will cross over. Read if you're a Star War Lore nerd.