The movies in-between acts are great. I'm into nightmare now and it's interesting to see how classes are diverging. Haven't really seen anyone doing the same things as me with the Demon Hunter. Also, I really enjoy the fact that the Male Wizard appears to have been voiced by the fellow who does Alucard in Hellsing. For that alone, I reckon I'll be picking Wizard on my next playthrough!
It seems harsh to compare Diablo to conventional MMO's as it isn't really operating in the same space. It offers a single player component. It isn't a persistent open world. Most gameplay areas are randomised. The core of the Diablo experience is going through the higher difficulties, which requires more thoughtful, strategic game play and the never-ending quest to find the perfect items to supplement your character/build. I know combat wise it probably looks like any other point and click hack and slasher, but the classes are all evolutionary steps from Diablo II really.
