OP seems to suggest the failing(s) of D3 are somehow tied to it not being an MMO.
^ This is utter nonsense.Imagine if it was, had huge open world and stuff. That would compete with WoW! So, the reason Diablo 3 sucks, is becouse of WoW. Blizzard didn't want to have another MMORPG-style game to compete with their WoW to begin with. At least that marks the conclusion of my analysis.
Diablo as a franchise is known for being the, "THE" defining game of the genre commercially and critically. The chances of Diablo 3 being an MMO are pretty low.
Also, Blizz are working on another MMO.