I think the whole assumption that Diablo 3 is a MMO is due to the internet connection requirement.
Torchlight 2 was fun. The much requested multiplayer feature got added. Dropping the gem refinement mechanic made players actually use less-than-perfect gems. Makes me wonder how the Torchlight MMO will end up.
And while I'm on the topic of Diablo-likes and MMOs, anyone taken a look at Path of Exile? It looks like Diablo-like MMO with a classless system (uses something similar to the sphere grid of Final Fantasy X).
I just started out on Path of Exile and so far I enjoy it quite a lot.