Re: vanilla dungeon design, I'm pretty sure complex design was the rule and not the exception - in addition to your examples I would cite Blackrock Mountain (most people didn't even run it because it was so big and convoluted, but raiding guilds had to do it because of the tavern event and to farm FR gear for MC), Scarlet Monastery (multiple wings even though it was pretty linear), Scholo, Living Stratholme (not Ustrat, that was pretty boring), even fucking Wailing Caverns was more complex than the room-corridor-room design that became the norm later on. Now, encounter composition and design is something else...