Regarding the classes available for Diablo III, I believe that something along these lines would be most beneficial for the game, thus giving those who play it a taste of both old and new.
Witch Doctor (Newly Introduced)
Paladin (Remade under different title with new abilities)
Rogue (Remastered to become hybrid of Assassin & Amazon)
Druid (Focussing on Lycanthropy and nature based spells, summons etc.)
+Additional Class TBA