OK, my group just fought through Thistletop level 2 (didn't get through what they named the "spikey-rune-pizza-coin-door" yet though....).
And we had a lot of problem fighting Nualia (through no fault of Watcher!'s excellent maps, printed out to scale), due to what I call the 'tactical geography' of the Thistletop dungeons.
They had gotten Orik onside, and he warned them that there was a trap in the corridor, that the previous bodyguard had "gotten messy" and so he got hired, and that if they were ever to interrupt Nualia, they had to call ahead to deactivate the trap. Our scout found the pressure plate, and they quietly dragged a table downstairs from the War Room and put it over the trapped area.
Our scout ran ahead and tried to open the door into Nualia's room quietly, but the Yeth Hound spotted him and sounded the alarm. This meant that combat started with the party quite a way away from the bad guys, with a 5-foot wide corridor and entrance into a circular room.
It took a full round of delaying for everyone to scramble backwards out of the corridor and back into the Hellcat's Hall, then the combat went back-and-forth down the narrow corridor, with Nualia retreating to heal up before our scout (very luckily) tumbled through her square and shot her through the neck with a lucky shot.
All I'm saying is, I like BBEG-fights to be a bit more party-friendly. I understand that dungeon corridors are meant to be defensively-built. If I'd though about this better, I would have changed things around a bit, maybe reduced the size of the hermit crab corridors and blow out the Observation Chamber into a big area that the whole party could participate in. As it was, I had my knight (the party's melee combatant) cowering in a corner due to tanking his will save against the Yeth hound's Bay, and one of the other players complained because she wasn't able to act in the encounter.