I haven't played Mass Effect in months, but The Arrival DLC brought me back to the Normandy and Miranda. THE REAPERS. Sorry, I meant the Reaper threat. 
 
The story beats are as strong as Miranda's thighs, with Shepard (and just Shepard) visiting a hidden human outpost in Batarian space to extract a deep cover scientist from prison. From her we learn more about the Reapers and their imminent arrival in the system. Can Shepard save the day? I'm guessing you know the answer, but at what cost? I love everything about the Reapers and the story hints here, along with the Twilight Zone style twists, hooked me.
 
The art direction is also quite good, particularly when you reach the hidden human outpost. They go out of their way to provide windows to see the world outside, much as Miranda's outfit provides easy methods for guessing at the body inside, and it's slick. The Shadow Broker DLC impressed me with how great the outside of the ship looked, and this one did it again. The last few minutes of game time are exciting. 
 
The time leading up to those last few minutes? Maybe not so much. It might be I'm too far removed from the story of Mass Effect 2, but the fighting and a few simple puzzles didn't grab me the way Miranda did down in engineering. 
 
Great story, great art, great that there's more Mass Effect, but the fighting was kind of meh. You know what else it needed? Maybe a different character from the crew along for the ride. I dunno, could be anyone really. How about... Jack? 
 
EDIT: Reapers not Collectors. Changed punchline to have 37.2% more tattoos.