I really enjoyed D3 when it was first released. I wasn't one of the ones bickering about the online DRM. However, I quickly hit a ceiling in Act1 of Inferno that would require me to switch from casually playing the game and farming items to intensely playing the game and farming items just to progress. While the gameplay is certainly fun, constant farming (with little to no forward movement) with nothing else to do in the game world becomes very boring.
Sadly, I think Blizzard will invest far less effort in resolving the replayability of D3 because it has no monthly subscription.
One other thought: They regularly take BNET offline for hours on end for 'scheduled maintenance'. It is a little mind boggling how they can do this - weekly - considering how most online service providers strive for five 9's of availability or higher. The issue is Blizzard has no SLA commitment to their customers. I can't imagine what they're doing during that maintenance window.