Having a beta and I must say, Diablo 3 is feeling, Diabloey....
The visuals are updated but still put you into the grim diablo mood, it's criticisms are overblown IMO, It's still dark and dusty, monsters are still twisted, deaths are still disgusting. So no worries their.
Sounds sound like they came from Diablo 2, which is a good thing as Daiblo 3 still has the eerie music which still sounds brilliant
Voice acting is brilliant, accents sound genuine and emotion has really been put though them, only issue is sometimes the dialogue can sometimes get a little... "Cheesy" (Act 1's first boss is an example of this)
Classes are disinct and all are fun to play! There are some balance issues IMO, as I had managed to play though the beta as witch doctor barley getting a scratch, but I'm struggling to simply survive the first part as Monk, I have not played as Barb, wiz or hunter yet, I'll give my opinion on those later
The biggest thong that is going to draw complaints IMO is the new command and health system, rather then simply lumping all your abilities into one big heap you then bing to left and right triggers, your moves have been pre-sorted for you though your keyboards and mouse so that specific spells are exclusive to the button it's assigned to this means it's easier to to use multiple abilities without having to cycle though anything, but also means that cycling abilities on the fly is really hard and tedious. Although I prefer it like this, there are going to be some hardcore Diablo fans that used specialized buttons and advanced keydinds to change abilities on the fly, will not like this.
Health and Mana are handled different:
Mana is now specialized to each class and all handle differently, E.g Monk's mana is called "Spirit" and does not charge over time, but, rather will charge though the amount of physical damage you do to a monster, this means that you can use your abilities constantly on large mobs, but you need to be in the thick of it in order to keep yourself charged. The witch doctor, however, has a small mana pool which drains and recharges quickly, and a cooldown on all but has primary spells, meaning that he can utilise his ability over long times without needing mana potions or a break from spells, but cannot constantly use a single strong spell all the time and conversely, cannot use all his power spells all at once.
Health is a bit different in D3, it is handled differently in the fact that they're is a much more limited amount of potions and that their are health orbs dropped by monsters.
Any questions, feel free to ask.