Most procedural generation threads turn into algorithm shopping lists, and the algorithm is rarely what went wrong. This is a writeup on the part that actually decides output quality, which is the structure you wrap around the random number generator.
Randomness Is Not Generation
A random number generator placing blocks at arbitrary positions produces visual noise. A procedural system that builds elevation from noise, runs erosion over it, assigns biomes from moisture and temperature gradients, then places vegetation by ecological rule produces something a player reads as a landscape.
The difference is that the rules encode design intent and the randomness only supplies variety inside them. When generated output feels wrong, the fix is almost always a missing constraint rather than a better noise function.
The Trade Has Not Changed Since 1984
Rogue generated dungeon layouts in 1980 so that each run was a new arrangement of rooms, corridors and monsters. Elite fit an entire galaxy of star systems into a few kilobytes in 1984 using mathematical seeds.
Both are the same bargain you make today: spend computation to save storage. What has grown is the pipeline, from a single RNG call to layered systems combining noise, grammars, constraint solvers and now models.
Determinism Is A Debugging Feature
The thing teams skip until it hurts is reproducibility. If a player reports that the world at seed 8815 was unwinnable and you cannot load exactly that world, you are debugging by guesswork.
That means every source of randomness has to run through the seeded generator, including the ones that sneak in later: hash iteration order, floating point differences across platforms, anything reading the wall clock. One unseeded call and the seed stops meaning anything.
Where Hand Built Content Still Wins
Generated content has a distribution and the bad tail ships too. Hand built content has no tail. That is why most shipped games run a hybrid: generated layouts assembled from hand made rooms, or a generated world with authored regions dropped into it, so the pieces are always good even when the arrangement is new.
Pacing is the other thing generators do not know. A generator cannot tell that the corridor before the boss should feel long.
Longer version covering the specific algorithms, noise functions, dungeon and level generation, wave function collapse, seeds and determinism, and where AI fits into this now: procedural generation for games