My group played Citadel, Speaker, and Spire, and in that limited group Spire was by far the most deadly. At the same time, we made that adventure last for months of RL time, and over time the dungeon changed as the PCs would get beat up, go away for a while, then return to find a new situation.
At the end, Gulthias had left the spire in the PC's flying ship (which he had stolen) along with most the denizens of the Spire that were his servants. And an NPC from my game had become chief of the Girallons, and were facing off against the vampires who had stayed behind, and their vampiric girallon servants.
And let me tell you something about a white four-armed magilla gorilla sized vampire -- THAT will scare the bejesus out of your PCs.
Anyway, it may have been a classic dungeon crawl, but we found it endlessly entertaining.
-rg