WoW stole everything it could from diablo 2 lol.
blizzard isnt intelligent enough to create something new and good so they had to leech from thier forefather's games. Thats not even counting the stuff they ripped off of everquest and other various MMO's
right now their mindset is very japanese... "take a technology that exists and 'make it better' "
the only thing that really disgusted me about WoW was how they gave a warrior class barbarian AND paladin skills and then leave paladins in wow with garbage support skills
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As for WoW and Diablo fans hating their "opposing" game, most people I know like all 3 franchises