So I ran this at PAX, and it was a blast. My table beat Ogremoch's Bane and took on the House Center, and we all had fun. I'm going to type up a report and post it, and when I do, you'll find a link here.
The Link!
On that note, there were a few changes I made to the module to help move things along quickly at the beginning. In the text, it says that Briddick has travelled with the PCs through the Underdark. Instead, I had a small band of svirfneblin deliver the PCs into Briddick's hands at the start of the defensive labyrinth. The whole module opens with Briddick asking the PCs to introduce themselves, and giving them an in-character summary of what's happening while he leads them through the labyrinth.
In addition, I used the labyrinth to build up some atmosphere, describing the stale air of the Underdark, the sound of things moving in the gloom, and the sprawled corpses of drow soldiers along the way. I even threw in an easy encounter with some zombies (which the PCs could opt to avoid), so they could have a chance to play a bit of combat early before they set about talking with the gnomes.
Overall, these things made the start of the adventure much smoother. In previous playthroughs, I found the PCs had too much to do right away, and not enough direction. Using Briddick as I did allowed him to suggest they go to see Kargien, and thus he gave them direction right away, while still preserving the option to ask around town.