>Keyforging. The ability to be able to choose what monsters will be in your key, if you have affixes like in WoW's mythic + keys where you'll have random effects such as aoe spawning on you for the negative affixes. But you could also get benefic affixes giving you for example a chance to reanimate a monster or some random and cool bonus like that.
>Better crafting. Outside of reforging the Diablo 3 crafting is boring. You can check some mods for D2 like Median XL to see how good it can be
>No more in-game cutscene. I know this one might look weird but I think that one of the things that made D2 and even Classic WoW more immersive was the absence of ingame cutscenes. They simply break the rythm and the surprise of the first encounter
>Having true farm road again like in D2 and not being forced to do rift. Rift should be rare and rewarding.
>D3 legendary effect and D2 style of stats.