If you felt Kasumi's Stolen Memory was too short and Overlord was too side-storyish, Lair of the Shadow Broker may be precisely what you're looking for in Mass Effect 2 DLC. According to BioWare, it's set to be the "richest in scope" of all existing add-ons, and also claims to bridge events of ME2 with any future products. So, even though BioWare won't admit this DLC pack will likely affect your Mass Effect 3 game, it was definitely giving off that vibe during our hands-on.
Why the lofty goals and promises of subsantial plot content? Because Lair of the Shadow Broker deals with ME1 co-star Liara T'Soni, the blue-skinned asari you probably "romanced" during the first game. When you bump into her in ME2, she's distant and preoccupied, and refuses to join your suicide mission so she can track down the mysterious Shadow Broker. Why was she behaving this way? Why the intense interest in the powerful, clearly dangerous Broker? That's what we expect to have resolved in this pack, as even its opening moments started to answer some of these questions.
The quest begins with Liara asking you to visit her apartment. Once you arrive, you find a crime scene with bullet holes in the windows and Liara nowhere to be seen. After some chit-chat with the on-site investigator (a Spectre, no less), you discover what had Liara so worked up about the Broker (we'll leave that to you) and set out to find her. After some shootouts, more dialog and a rather difficult boss battle, Liara joins your party and the DLC continues. At this point, which was roughly 70-90 minutes of gameplay, our BioWare rep said we were about 40% through, so it's already longer than Kasumi and on track to out-last Overlord.
The biggest surprise was the Episode II-esque car chase through the floating roadways of Ilium. Here you're screaming across the night sky, zipping in between buildings and avoiding oncoming traffic while tailing someone involved in Liara's Broker dealings. It's a brilliant idea, but I felt the hover-car handled a bit sloppy, leading to more than a few unintentional collisions. The chase is also quite short, so it makes me think even BioWare knew it wasn't hot stuff - if they felt they had a slick new gameplay idea on their hands, surely it would have been featured more than a few minutes. It's certainly not a total mess, just not up to the usual excellence seen in the rest of the Mass Effect world.
But should you buy it? 800 points seems like a reasonable price given that the campaign seems longer and more substantial than Overlord, and if the plot ends up actually affecting the main characters in a noticeable way, then it's almost a must-buy for franchise fans. There are also some other small bonuses, like new powers for Shepard and special dialog if you have an ME1 save game with Liara romance data on it.
Short version: biggest, most robust offering yet, buy it even if you found the others lacking as it should actually have some ramifications. Shame none of your teammates talk during the DLC packs, even though we understand why that is - BioWare's official response says the DLC packs are about certain characters, so the teammates are peripheral in those instances, but more likely it's because hauling in 13 voice actors to record brief snippets is quite a hassle.