Best piece of DLC
Without a doubt, the best DLC is the alternate costume pack #2!
No wait, what I meant to say is Lair of the Shadow Broker.
There's actually a lot of terrific DLC for Mass Effect 2- Arrival and Overlord are pretty bitchin', but come on. Nothing holds a candle to Shadow Broker!
I think of it a bit like Shepard's loyalty mission, particularly if you're in a romance with Liara- helping her out and taking down the GD Shadow Broker helps clear Shep's head for the suicide mission.
The gameplay is varied, the locations even moreso. There's humor, drama, romance, and a never-before-seen alien species. There are a couple of boss battles, including one against fellow SPECTRE and all-around BAMF Tela Vasir, who cuts Shepard down to size in more ways than one.
Then there's Liara herself, who has gone through a great deal of change in the two years since the events in Mass Effect. She's become her own person- one whose plans may not always align with Shepard's any longer. Focused on revenge to the point of obsession, Liara has hardened and become a total badass in her own right. And I love- love- that the major plotline of the mission is a "damsel in distress" scenario, and for once it's a woman doing the rescuing of a man- and that it's not her boyfriend she's out to save. It may seem like a small thing, but BioWare has flipped gender (and genre) conventions on their head.
On top of all the great story and combat, Lair of the Shadow Broker sprinkles delightful goodies all over the player once you've taken over the Broker's base, in the form of moolah, resources, crew member dossiers that provide huge amounts of insight into everyone on your squad, and surveillance videos from around the galaxy, which are often good for a laugh.
Lair of the Shadow Broker isn't just my favorite piece of DLC, it's one of my favorite missions in all of Mass Effect.