(Guess I'm slightly necroing this thread, fun topic though!)
As a dev I really like the idea of my game being able to suprise me, so I keep playing with procedural level generation.
This basically just slaps a bunch of predefined rooms and corridors together in ever-branching paths. Of course you can see the repitition cause there's only like 8 pieces so far, and it doesn't connect back on itself (yet!!), but I like how this can build multi-level structures.
My last generator was able to loop back on itself, but it was a perfectly flat single level, and the room were only different in terms of being 2x2 instead of 3x5 or whatever. Not bad, but I like how much room this gives me to hand-craft stuff, while still keeping players on their toes and keeping them from just memorizing their way to mastery.