Whizbang Dustyboots
Gnometown Hero
I'm an old school gamer myself (started with 1E back in 1979), but I think that the old school system worked as well as it did because A) it was mostly adults doing the new cool thing, B) many of them soon had a financial stake in the game doing well and were more likely to show up regularly and C) they weren't competing with videogames and the internet, which tend to steal away more casual players.That's sort of an interesting approach because the old school style specifically wanted a mega dungeon, well, just a dungeon in those days, precisely because it wasn't something you could complete.
So the gameplay loop was that A group would explore a part of the dungeon and then have to leave, And the next group could either pick up where they left off or explore a completely different part. Hence why time tracking was so important (if group a doesn't explore a room and group B explores at the next day then when group a gets around to exploring it, they're going to find the treasure has been taken already)
That's said though I'm not completely married to the idea of the mega dungeon, especially because I would have to design one...
For a non-store game, having an open table game chip away at a megadungeon (Temple of Elemental Evil, rather than the moathouse dungeon, for instance) is fine. But if you can't guarantee that even a single person will show up more than once, unless you really love that dungeon, I don't think the continuity buys you much other than extra bookkeeping. In contrast, I find that smaller Five Room Dungeon adventures have much lower cognitive load as a DM.
But there's also no wrong answer here. If what would be the most fun for you would be to have your players chip away at the dungeons below Castle Nobleshield each week, like Gygax and Arneson had their players doing, that's great, too, and I'm sure players will enjoy it.