OD&D recommends prepping six dungeon levels (as a minimum) before play begins.
Sure. But once you have that in hand you can bring in new players on-the-fly and run dozens of sessions with little or no additional prep.
My point is that you need to get away from the concept of putting together a group of 5-6 players who are expected to all get together on a regular basis for a dozen or two dozen or an indefinite number of sessions.
There's nothing wrong with those types of campaigns existing. But that level of commitment is obviously off-putting to new players.
I'm speaking from immediate experience here. I've been playing in a campaign run by a guy using the
Caverns of Thracia as a megadungeon. There's been a persistent continuity across a couple dozen sessions, but because each session is a separate excursion into the dungeon there's no need for the same group of people to re-assemble at every session.
Juggling schedules? Not a problem at all. The DM posts a date on Facebook, invites a dozen-plus people, and whoever can show up for that session shows up and we play.
Inviting new players? Incredibly easy. They're not making a commitment beyond a single night of playing games with friends; and we're not left hanging if they decide it's not for them. We've introduced lots of new players to RPGs since we've started playing, and quite a few of them have stuck around for second helpings.
DM's prep time? Apparently he read the module in about 3 hours and started running it. Minimal or no prep between sessions. Certainly designing a complex like the
Caverns of Thracia would take some time, but that's why a good introductory game would include a ready-to-play scenario.
Imagine if
Monopoly expected or required you to get together a group of 6 players who would need to meet regularly on a weekly or bi-weekly schedule for 20+ sessions. I can virtually guarantee you that
Monopoly would be a much less popular game.
I'm looking around to find similar easy-to-organize, easy-to-invite formats for other games.
Shadowrun looks tempting: Although it would require a lot more prep (since it lacks OD&D's procedural methods of content renewal), if the player body were all understood to belong to a single organization of 'runners that got contracts which just happened to be fulfilled by whoever showed up that evening to play, you'd get some of the same social network effects.