Greyhawk was basically a rules booklet that introduced Paladins, Rogues, different sized HD for the different classes, 7th-9th level wizard spells and assorted monsters and magic items. There was nothing campaign-specific to it.
Blackmoor came next, and it had the Monk character class, a system for assigning different proportions of your hit points to different locations (extremely lethal, I never knew anyone that used it), the "Temple of the Frog" adventure, which was utter rubbish IMO and incorporated elements of techno-magic.
(Eldritch Wizardry was the next one, and that had Druids, psionics and demons if I recall correctly. I never owned that one though, only the first two).
All of these were really rules supplements, the "adventure" in Blackmoor was too light to be considered a proper adventure, and could be set in any old swamp.
EPT was a great campaign setting, but it wasn't D&D (Attributes were rolled on d100 for instance).
One of the big advantages that RuneQuest had when it came out was a richly detailed world which sparked off lots of thoughts and ideas for adventures - it was one of the things which originally drew me and my players away from D&D back in about 1977/78. I sometimes wondered whether the decision to publish campaign worlds (whether Greyhawk, Forgotten Realms or whatever else) by TSR came as a response to that. Maybe not directly, maybe it was just additional revenue streams
Just a little bit of extra info from someone who was there
