Even a Sith Lord like Darth Vader has a boss he has to answer to, and when he failed at his last assignment which resulted in a Death Star going KERBLOOEY then he sure wasn't going to pass that next performance review. 
 So Vader is really in the Emperor's dog house which results in him suffering a demotion and having to take orders from an Imperial officer who sees him as simply a weapon to be used. However, Vader also has his own agenda like finding out exactly who was that Force-strong pilot who blew up his shiny new Death Star. 
 This shares a story line with the main Star Wars comic that Marvel has been doing, and I very much enjoyed the first half of this which brought up some plot points that I had never thought about like how the Emperor probably wouldn't have been very happy with Vader after the events of A New Hope. The second half fades a bit because Vader uncovering a secret program that the Emperor has been hiding didn't seem like anything special. 
 I also thought the new droids Vader acquires, Triple-Zero and Bee-Tee, were a nice touch since they're essentially C-3PO and R2-D2 if they went bad and developed a taste for torture and murder. 
 It was entertaining and did find some new angles to probe with Vader as a character and his role as the Emperor's enforcer, but it felt like maybe the highlights should have just been put in the main Star Wars book rather than being it's own title because it did start to feel thin after a while.