The only games that really shared similarities that were so strong were Everquest, WoW, and Aion.
Everquest I can't account for why, is so similar to WoW. WoW's interface is simply channeled mostly from Diablo II's, and Aion, well, Aion just seemed to copy the biggest most successful MMO in history, (WoW) which is a smart move right? The best business model for them would be to take que's from the most successful competitor.
WoW is based off EverQuest, since that was one of the first big proper MMORPG's out there, and I still think EQ (and EQII) is much better than WoW. I played EQII recently and WoW is just so ridiculously dumbed down and simplified in comparison... >_<
DII was based off D1. LOL