I know it's not D&D, but the most fun killer-dungeon I've had the joy of was the Tomb of Iuchiban in Legend of the Five Rings.
For one thing, you know going in you're going into a tomb designed to trap a body-stealing blood sorceror, imprisoned in its walls. You know enough of his backstory to know how Bad it is.
It's been years since I've played it, but I remember the 'Fear the Goblin' room -- it was an arrow trap, if I recall correctly -- and the next room, which I managed to somehow get into alone. The trap in that room required that you step on tiles in the order that the Kami lost the tournament to see who'd rule the Empire (the Kami were the children of Sun and Moon, crashed to earth) The difficulty? It's a puzzle for the player, no one can help, and at no point in any of the sourcebooks etc, does it explictly say which order they finish in. Each clanbook would talk about their founder beat this sibling, but lost to that sibling. So, it was a lot of detail work and worry.
The other cool part I remember is the Heart of the Tomb. Basically, when you reached a certain part of the dungeon, you began drawing rooms at random to see where the Heart put you. Some rooms would and could reset, and you had no guarantee of getting to the 'End'. It was the spirit in the Tomb playing horrible tricks.
And also consider, you can't heal naturally in there, and you cannot regain spells inside the tomb.
Good memories.