Comments on the Megadungeon format question posed by a fellow blogger at Grognardia a few weeks ago:
My favorite megadungeon format the "Ruins of Undermoutain" boxed set:
Large poster map for the dungeon
Book of special keyed encounters
Book of random role-up encounters to fill in the rest
It's pretty close to all you need.
My least favorite megadungeon format "Return to Undermountain"
Everything in one book so you have to flip back and forth between the maps and the encounters
Map arted up to make them unreadable and CROPPED!?
No non set piece encounters, as matter of fact everything off the linear railroad plot blocked off with rock falls to ensure no "sandboxing" ever
As my friend refers to this module "a little tiny crappy piece of Ruins Undermountain"
The second edition large boxed sets remain some of my most favorite adventures the "Ruins of Myth Dranor" is a close second to "Ruins of Undermountain" although it is not a classic megadungeon. The one thing Myth Dranor adds to the repertiore is the mini-dungeons on cards which gives the DM some flexibility, however I recommend against printing the key on the back as this leads to a lot of card flipping.