When building card games I've worked on a system that generates levels based on...
Difficulty: Generally just depth. I've failed at this so far.
Environment: Just a tile set really, lava instead of water. Trees instead of walls. Affects 'wandering monster' list and some enviro hazards.
Architecture: Cave, Dungeon, Castle, etc...tends to control which traps and some hazards. So far environment and architecture are linked, hard to separate with cards.
Boss: Boss of that section of the game controls which minions your find.
Loot: You want the loot to be boss and minion specific, and the treasure chests to be enviro/architecture specific. Like the "Skeleton Key" only pops up in the dungeon architecture and only from a high level minion serving The Bone Lord...for example.
Achieving linkage like this is vastly different for card games, but I did it through various small decks.
1. Dungeon Decks: 18 rooms per environment. Ice level, fire level, dungeon, cave, castle. Rooms can have 1 to 4 entrances. Some doors are locked. Sometimes there's a big treasure chest or a 'wandering monster' that you only get one shot at before he wanders away. 1 boss room, enter at your own risk. Some 'hazard rooms' like pits, lava and such (agility challenges, roll to jump/dodge/duck etc...)
2. Boss Deck: 5 Different bosses so far. Draw this at the beginning of the level so everyone knows which boss they'll face. Find the boss room to fight him. Beat him, beat the level, and take his treasure (artifact!).
3. Artifacts (boss loot): About 20, tried to somehow link these to the bosses, but haven't figured it out yet. If you beat a boss you draw an artifact. Yay! Maybe I'll have small decks of 5 artifacts that go with each boss...hmmm....
4. Monster Decks: 5 different decks of about 20 monsters. Each linked to a boss thematically (Balrog boss has demons, The Necromancer has zombies, etc...) Enough for one monster per room and then some. Players draw a monster per room, this card stays on the room until you beat him. He has treasure with him depending on his strength. Beat him, win the treasures AND passage through the room. Fights are simple Roll and Add Bonuses, miss too badly and you die (Knocked out really, go back to the beginning and restart, lose a treasure. Or play hardcore...death is final).
5. Treasure Deck: 100 treasures. You basic armor, weapons, magic items, consumables, etc...
6. Character Races and Classes: Still working on how these will work...original characters were based on porn stars. Ron Jeremy the Dwarf, Belladona the Sorceress, Peter the Northman, Penny the Flame Witch...and Jeff Stryker the Pirate (he's a gay porn star...hilarious...pirate...chuckle)
Ramping up of difficulty is virtually nonexistent, but the challenge is in beating the other players.
I outline this here as food for thought on how to build dungeons, I think it's strong in linking minions to bosses and hazards to the environment. I'd like to be able to link bosses to the environments and vary the architectures, as well as linking treasure to the different minions...but there's only so much you can do with a tabletop game before it starts to get incredibly wonky.
-Jo