Greatswords were simply called two-handed swords in earlier editions of D&D, they were not new for 3rd edition.
Comparing AD&D 2e and D&D 3e is a bit like comparing eggs with bacon as the combat systems are different. They dropped weapon speed and rules for close-quarter fighting, for instance. In 3rd edition, greatswords replaced two-handed swords in that sense that they'd be the next bigger sword from the longsword, while bastard swords (huge long-gripped longswords that could be fought with one and two-handed styles), claymores (shorter Scottish two-handed sword) and proper two-handed swords disappeared.
Since they didn't come from a plant, individual weapons differed widely, but your typical historical two-handed landsknecht Zweihänder swords often had a rather large ricasso, so you could grab the blade without cutting yourself. It would mainly see service against other unit types, like pikemen and cavalry after the first line had fallen. Shorter zweihanders could be strapped to the back of a tall mercenary, the really long ones were carried over the shoulder, like a polearm. The original description of the greatsword in the 3e Player's Handbook doesn't link it to any historical examples, give any description of how it looks or even state a length: "
Adventurers recognize the greatsword as one of the best melee weapons available. It’s reliable and powerful." Perhaps it's my personal disdain for 3e, but the greatswords in BG3 look exactly as the caricature rubber clubs I always pictured.
