Then, in what ways are you working with more modern gaming styles?
I guess, strictly speaking, I'm not. But I think what is different from how I might have run a dungeon in the 80s compared to the campaign that I'm running now, is that there are many plots. But it is not like there is a specific storyline to follow. In addition to the huge number of locations and possible encounters that are highly interlinked, there are different factions with different goals, a lot of history, a lot of potential plots and quests. But what the story becomes is entirely up to the players. Initially, it can be a bit disorienting for players used to more modern story-driven adventures. But what quickly happens is that plots emerge and take on a life on their own. They have a story to follow, but that story never had to be the story. The decisions and actions of the PCs decide the plot.
What I do think is important for many players is that they have a reason to go into the dungeon in the first place as
@iserith stated in an earlier post. But after a few sessions, reasons to continue going back emerge. After a few sessions, I don't find that the mega dungeon has any less story than a typical modern adventure.
Other more modern preferences work just fine in a mega dungeon. You don't want to spend large amounts of game time explaining in detail how you are searching or how you deal with a trap or locked door. Passive perception and skill checks can be used. You really like spending time acting out your character in social interactions, there are opportunities for that. You don't want to try to draw out a map as you explore, there are VTTs that will clear fog as you explore. You want normal XP earning, that works fine. Lots of things to kill in a mega dungeon. Milestone leveling? Sure, when you reach a certain area or defeat a certain foe then level up.
I have trouble thinking of anything that would really prevent newer more "modern" players from enjoying a mega dungeon, other than they don't like the setting. But that can be an issue with any setting or adventure.