D&D for Grown-Ups: Megadungeons for Episodic Play

To recap, my goal is to get myself straight back into my hobby, and to get my friends into an adventure, all despite the fact that we are time-poor and my friends find it hard to commit.  I want to set up an episodic play space in which varying players and their characters can meet to adventure (open table) but where the threads all ultimately tie together into a satisfying shared story created between them.  A megadungeon seems like a great option for this: an adventuring environment that is both contained but also immersive - a great combination of manageability for the GM while allowing lots of meaningful choice for the players.

Each play night a different party assembles in the nearby starting base (ala B2 Keep on the Borderlands) and plumbs the depths of the megadungeon for a session, before falling back to the safety of the base (hopefully) laden with treasure, tales of derring-do and tantalising hints of the riches and secrets yet to be revealed.  Most old school systems/retro-clones use treasure as XP so there is some incentive and reward for those players who have their characters make regular forays into the dungeon.  The idea of "balance" is less of a concern in old school play and I suspect (hope?) that this sort of thing will even itself out - lower level characters should be able to either find appropriate challenges in upper levels, leaving the lower levels to more advanced characters, or else could join in with higher level characters as henchmen and reap the rich rewards and meteoric climb if they manage to survive.

Now I would like to learn how to run (and eventually design?) a megadungeon by starting with an 'out the box' published option - which has the additional advantage of allowing me to get into it pretty quickly!  Fortunately, while megadungeons are relatively few in number the OSR has produced several which hare highly regarded and which I have already picked up:

1.) Stonehell: The premise is that a long-defeated tyrant once forced his prisoners to dig their own prison which eventually developed into a sprawling dungeon which in turn attracted all sorts of foul denizens to dwell therein.  Based on a layered "one-page dungeon" format for ease of use.

2.) Barrowmaze: As the name suggests, a sprawling maze beneath a moor dotted with Barrows, plagued by several factions and hordes of the restless dead.  Multiple entrances and exits through surface level barrows and some simple but effective mechanics which fit the theme beautifully.    

3.) Dwimmermount: James M's ambitious science-fantasy megadungeon project, brought to fruition in meticulous detail by Alex Macris of Autarch - this mountain megadungeon literally serves as a 'tentpole' to a campaign, and plumbing the dungeon's depths is to plumb the history of the setting itself.

4.) Anomalous Subsurface Environment: A gonzo, post-apocalyptic mega-dungeon and setting.  It is highly imaginative and filled with great ideas but just not the flavour I am after.  Perhaps I could use it as a chassis and reskin it though?

Are there any I am missing from this list which you feel I should consider?