That was a joke. Laugh now.
I'll go right ahead and mention Durlag's Tower before any of you dopes do, because at this point we all know what makes it a fantastic dungeon. To me it's the perfect blueprint of how to make one. Good dungeons tell stories or give you the hints to piece it together.
It doesn't need to tell the story of the dungeon itself, it can also just be the setting of a story. Take the Ineluctable Prison from Wrathfinder for example, the best dungeon of the modern age. You get the lore of the place but the adventure is about busting your friend out of there and witnessing an internal power struggle for control of the prison (or you don't, depending) and find some interesting inmates with cool quests. That dungeon tells several stories in fact.
PST's "dungeons" barely qualify as such but boy do they tell stories and that's why they're great. Who can forget the "Don't trust the skull" moment? Or getting mazed and finding your journal made from your own skin and bones?
Bad dungeons are those that don't tell a story. They may be rooted in the context of the world in question and have a certain reputation, which is often enough to be honest but then you go inside the dungeon and it's just really unremarkable. I remember how godawful the dungeons in Tyranny were, not only because they all look the same but because they didn't engage you narratively at all. They have lore and history but once inside all you do is fight wisps and do a shape puzzle at the end. One dungeon attempts to tell a story; there's a dying dude and he wants you to find his fadda's sooard (or smth I don't remember). You then find it in 2 minutes, return it to him and then he dies. Riveting stuff.
Mechanically, you need to find loot. Good **** too. Stuff that would warrant being lost or hidden for centuries and then dug up. If you don't leave the place with at least one new useful item, something's gone wrong.
