At one crucial point there was a turning point for the entire hobby. Before most in the hobby even knew it existed, before many of us were even born. It was before the supplement 1: Greyhawk was released.
The bad news, Greyhawk ushered in the era of bloat and garbage that plagued D&D through 1e, 2e, 3e, 4e, and now 5E. Yes there were other editions but Greyhawk was really the crux that made OD&D into the precursor of AD&D1. It could have gone another way, there could have been work made into revising and expanding the game intelligently to resemble B/X that came out nearly a decade later. But that didn't happen and here we are.
Things debuted in Greyhawk
Thief Class
Paladin Class - a ridiculous Mary-Sue class that was stupidly powerful
Demihuman multi-classing (as opposed to it just being an Elf thing)
Strength adding to To Hit and Damage for attacks, encumbrance, Open Doors
Intelligence adding to spell use, etc
Constitution adding up to 3 HP per level
Alternate HD for classes (used to be d6 across the board)
Racial bonuses for Thief skills
Weird bullshit regarding weapons vs armor having a pointless bonus or penalty to hit
Weapons using different damage dice (used to be d6 across the board)
Weapons doing more damage to larger opponents (eventually dropped in 4E because it was always stupid)
Alternate damage dice for Monsters (used to throw d6s only)
Bunch of extra stupid spells for MUs (Delayed Blast Fireball and Monster Summoning, etc), Clerics get like 4 including the brilliant Speak with Dead
Stupidly powerful magic items including such PC nut busters as the Holy Avenger and Deck of Many Things (in a completely random order because fuck finding anything)
Absolutely ALL of the shit in Greyhawk was bad for the game, expanded complexity without increasing fun in any way. Thieves took away the ability for other classes to attempt dungeoneering, as now there was a fucking class for that. Multiclassing became a thing all demihumans could do, ultimately ignoring the actual point of classes in favor of fucking twinkery.
Ability scores became more important, and more ability scores became important for Fighters than other classes because fuck Fighters (a sentiment carried on until... forever. It was carried on forever).
Tossing ALL the die types into the game was done because "we got these dice here... whaddya you want to do with them?" They're not really used in a useful or necessary way.
Options for spells and weapons are expected, but man are these just the most unplaytested trash additions I've ever seen. it all comes down to something I have to say...
Greyhawk was obviously scraped together in a few months from houserule/homebrew notes because D&D started selling like hotcakes. Why sell one thing when you can sell a now "required" supplement to get the "full game." D&D's line began with a shameless cashgrab.
And if that cash wasn't grabbed, then the hobby wouldn't exist. So, I mean, thanks Greyhawk.
