D3 is a dumbed down version of World of Warcraft, and WoW is already pretty dumbed down.
But still, the biggest problem with D3 is it's just not a satisfying game to play. You farm and farm to beat inferno. Then you farm and farm, getting drop after worthless drop that RNG's poor stats and isn't even worth selling, just to get into later acts of inferno. There you farm some more again. You're literally just farming, spending real money, then farming more. It's like WoW accept you're farming the same content over and over again, and you're playing, for the most part, by yourself.