The ability to build a good, powerful, functional build on every class and for every class to be on par with the others…
A Paladin.
Runewords that actually create new powerful items.
About 3 times as many Uniques in the game that grant people the ability to define builds and make them functional (again, for variety).
For those uniques to drop for all classes so we can farm for items on a main to make builds on alts.
For us to have no RNG with masterworking except for the roll on the stat we want (in other words, PICKING the stat we want and having the range be RNG rather than if we can get the stat we want).
For enchanting to offer 4 options instead of 3.
3 times as many Aspects to let us create and engage a variety of builds for each class.
More events to occur in dungeons to make them more enjoyable to run in the hopes of finding those events. (as in, scripted, fun, mulititasked, layered events that occur randomly and you never know which one you’re going to get in the run).
More body options for all classes. (If I want a thicker in the middle sorc, so be it. If I want a tall slim ginger Druid like in D2, so be it . If I wanna be a skinny but cut psycho looking barbarian, so be it.)
The ability to unlock the nice transmogs from the store with in-game effort. Let’s face it: the store Transmogs are far, far, FAR better looking than literally everything we get for free and it’s a crime. They sold us on that not being the case, but here we are.
Entire new skill trees for every class. Fire tree for Druids. Arcane tree for Sorcs. Sentry/Grenades for Rogue. Amphibian/Frog/Water based tree for Spiritborn. More thrown weapon options for Barb. Poison/Disease tree for Necro.
More mastery passives for each tree for each class that unlocks more ways to play. (Fire/Lightning combo mastery for sorcs, for example).
A horadric cube that lets us convert things on the fly with recipes and options.
An entire whole different map to explore Hell as its own world.
I could go on.