I will say ONE thing that's not going to win favors from WoW fans (fans who ONLY have played WOW, and not previous Diablo games). is that those who like the "sandbox" features of WoW or a game like Skyrim might find themselves very bored as there's really nothing else to do other than kill monsters/collect loot.
There's no fishing, cooking, herbalism, mining, archaeology, pets, factions, minigames, vehicles, daily quests, reputation rewards, mounts, ect... it's just better gear and killing monsters add-nauseum.
I also question how many will want to play past Normal mode... I mean, look at WoW - it's already hard enough to encourage players to beat Heroic Mode without getting bored... and that's just difficulty 3! How many of them are REALLY going to run through every act 3 times on different characters on different difficuty settings... and then expect them to run a FOURTH difficulty without being sick of seeing the same damn things.