Just like I did for Doom 4, I will now post things that must be in Diablo 3 to make it a Diablo game:
Clearly, hordes upon hordes of beasts with awesome art and brutal and gory death animations to kill.
Dreary, atmospheric *GUITAR DRIVEN* music. Who doesn't get shivers from hearing the original Diablo town theme or the Rogue Encampment theme from DII?
Ridiculous arrays of loot, including randomly generated item stats (I'd like to see this on even the best gear as well). Really adds to a sense of uniqueness.
3/4 perspective. I do not want third-person WoW/Diablo MMO camera. I want fucking 3/4 perspective. Just because today's computers can render the face of God in .03 sections at any angle doesn't mean everything has to be third-person or first-person. Give me the goddamn 3/4 perspective.
A reference to cows that will make me laugh.
The return of the chat gem in some form.
Now that that's settled... what NEW things would be cool in Diablo 3? Things that are new to the series from a gameplay or technological standpoint that would fit in with the Diablo universe.