I don't think I could live without potions. My barb just can't handle any respectable mob without using three (level 21 in the start of act 3, roughly 400hp, that's half the amount my level 69 act1 hell necro has, resists chosen depending on what damage I'm gonna be facing, drawing people off and fighting on my terms, using warcries intelligently) and my necro can't do anything without quaffing super mana potions like a dodgy radiator goes through water. I don't want to play a game where I have to put any points into energy.
I don't think I like the idea of a cleric style support class either. The way in diablo 2 you have three and a half classes that do well as support, three and a half that are excellent tanks, and nearly all of them doing great damage, all in different styles and every class (except I suppose the sorc) falling into at least two categories was what made the game so good and replayable. Having classes fit one single style would take all the fun out of it.
I really hope they don't dumb it down at all. Or at least don't hide the underlying ruleset or go to boring timers on skills. I loved looking up in tables what ias breakpoints I needed to cut another frame off my attack speed. I loved playing odd or novelty builds (<3 bowadins, melee sorceresses, daggerzons (really my favourite tank ever, I might make another and not lose the save before she dies this time) and such) that just happened to almost work well because of some nuance of the ruleset.
Other really short points that I can't be bothered making into paragraphs:
I hope static items like uniques and sets aren't tremendously better than the best of the randomly generated rares.
I hope the horadric cube makes a comeback and there are more, less static crafting recipes.
I'd love to play hardcore right from the start.
At a guess there will be five classes, and if they're taken from the acts in d2, what would act 4 give you?
Barbarians are silly
I hope d3 isn't too influenced by wow. In the style of quests, the way pvp works, the way items happen, the way skills work, the gang dynamics, everything.