Played both betas, level all chars to be sure about conclusions. And I played a lot of arpg’s and MMO as hardcore player.
This not a hate post, the game is not terrible, it is kind of good and with great potential, it is just not a level of AAA game at least for now, and with small quality of life improvements it will be much better.
Here is the list what I saw by myself and from most of other players so far.
-Overlay mini map and route build inside the dungeons
-Better interface design, saw some fans work how it could looks, even that was much better, add resists stats to character sheet, comparison of all same type items from both slots, not switching between them. Add tooltip for fast skill panel (default S button, but takes a while to find it)
-Add option skip all dialogs by default (for first playthrough is great, but when you play another char that’s already annoying)
-Add click to move button combined with picking up the loot, and main skill split
-Add at least 2 more slots for skills, I do believe it is made for console players, who is lack of buttons (no offence), but why everyone else should suffer? It is just ridiculous when you play for necro and 2 of 6 slots taken by skeletons and golems, and you play with 4 buttons, like some stupid mobile like game. Also never take a ult ability, just because no space for big cooldown ability.
-Background music is nothing special, not memorable at all, never have a wish to hold on with fight just to listen some nice motives.
-Lags, I did play with permanent lags with unknown source.
-Itemization just boring, never check the items if it is not legendary, just wear what is better by deface\damage+1 to skill, all blue instantly thrown out of stash. Give at least any reason to use a blue items. Sure it will be less problem at higher levels, but still could be better.
-Add more customization for character creation, at least more faces, etc. Can learn from Baldur’s gates 3 
-Talent system is weird, not bad, but never left a feeling about something wrong with it. Maybe that’s because of lack of skill slots. In overall just OK.
-Add min\max caps for zone levels, without that players will never fill hardcore or overpowered.
-Add single player mode (probably will never be, but need to mention).
-Some animations looks weird.
-Balance improvements, buff necro sacrifice abilities. With one legendary and make build around it I become immortal killing machine. Similar for sorc it was with double hydra, but still far from necro.
-World activities, far from typical MMO, and already not a classic diablo playstyle, idea not bad, but realization is grab a lot of bad things from both and combine. But about this personally I am fine.
And what is definitely and only good parts, is graphics and overall atmosphere, armor sets and weapons looks cool.
Some of the points definitely discussable, and maybe be fixed before launch, but c’mon, for sure should be at least fixed interface, skill slots and level cap, that would be fun to see how game will burn in hell without at least this things.
Anyway for now still fills like I played a alpha, than beta. And I would take half year - one year of development more. But lately blizzard release half done projects, which kind of sad.
Let’s see. Hope Bliz will se my topic, lol