The Emperor holds Darth Vader responsible for the destruction of the Death Star and questions if he is still relevant or even still worthy of being his apprentice. Vader must prove his relevance, deal with the ambitious wishing to take his place and find out who this rebel boy wielding a lightsaber and responsible for the destruction of the Death Star is. 
 I was hesitant to read this as the iconic Darth Vader is often more menacing when he doesn't speak or uses very few words, and we don't know what he's thinking. I haven't read much expanded universe with Darth Vader but this feels like the best interpretation outside of the movies. 
 Some of the B plots felt a bit out of place for the character but are necessary for the narrative. The ending is a brilliant scene adding depth while staying true to the character 
 I recommend it to anyone interested in Star Wars cannon. We start to see how Darth Vader leans about Luke and who he is.