That 15 square corridor leading up to the New Master's Lair? That's bland and uninteresting.
That said, this is the ultimate encounter of the Moathouse. Lareth the Beautiful, the leader of the cult, lives here, and he's got a sizable entourage. The guy himself, Drex (a dragonborn soldier), three Human Guards (statistically identical to the bandit leader Enzer, who the PC:s likely fought earlier) and a shedload of minions. Some of the minions hang out in the abovementioned corridor, theoretically slowing down the advancing PC:s while the Human Guards poke them with their halberds.
In practice, the fighter blasts past them with an action point, bringing the fight into the proper rooms. A battlefront sets up, and Lareth steps out and says something nasty. Then he charges in, critically misses, and the party unloads with their dailies and kill the poor guy in one round. Or maybe that was just in my game. Rest in pieces, Lareth the No Longer So Beautiful.
Moral of the story: If the party takes a second extended rest right before assaulting Lareth's chambers, follow the advice in the module about adding enemies to the Moathouse. I did, but a single extra Barghest (recently arrived, now pissed about the deaths of his bugbear friends) didn't change much. If you're feeling adventurous, do what I considered and have everything that still breathes set up an ambush in the courtyard. Maybe toss in the Giant Crayfish if the PC:s didn't kill that earlier, removing some minions and maybe a guard because the desperate plot to capture it took a toll on Lareth's troops. Oh lord, why didn't I actually do this, it sounds like such an awesome fight in my head.
All in all, this wasn't a bad fight. To be honest, real life intervened and I didn't get to finish it (but at least Lareth hit the dirt before the game broke off). If there's anything I'd complain about, it's that the room is kind of small, but it worked okay with the melee-heavy NPC group and the almost equally melee-heavy PC group.