Wayne R over at Initiative One is making his own megadungeon.
Why Build a Megadungeon in 2017?
I understand the pull - both from an open table and/or pick-up campaign perspective, and from a general GM prep perspective. I said as much there, and in the past, why I think megadungeons are good for a low-pre-session prep game (once the dungeon is "done" enough to play) and why I think it's easier to run your own.
This isn't news for anyone who's read my blog for a while or browsed my page of megadungeon articles and links.
I think making your own megadungeon is rewarding. If your players are game to try, and especially if they're game for focusing on what megadungeons do well (repeated delves, exploration, weirdness, ease of getting to the killing-and-looting, etc.) and not what they don't, it can be fun. I think it's more fun than it looks from the outside, as well. It's easy to dismiss megadungeons as impossible or not-fun without trying them. And it's hard to just give your own megadungeon a shot for 2-3 sessions just because of the sheer scale of prep - once you start one, you're committed for a while or you've sunk a lot of costs.
But once it's going and people are enjoying it, it's very satisfying and interesting. The game system doesn't matter as much as you might think - I'm running Felltower in GURPS, and I'm not sure anyone else is doing so (maybe even, has done so.) Systems like original D&D and B/X D&D and AD&D 1st edition are packed with tools that assume a megadungeon. Clearly 5th edition D&D needs fewer monsters per PC but can handle big dungeons, so why not megadungeons?
By the way, this is no knock on existing megadungeons. If you can digest someone else's dungeon faster and easier than you can write your own, that'll be faster prep. You'll have name recognition and that pride of dealing with a known dungeon, too (my players are justly proud of having bested White Plume Mountain.) And other people's megadungeons are a great source of material to raid for your own.