First of all, calling this a Beta is a gross misrepresentation. When you release something for free that only includes the first chapter of the first act, that is called a demo. I'm extremely skeptical of the actual testing usefulness of this beta with only around two hours of gameplay to be had per tester. Ten, I suppose, if you play the same chapter five times to see each class.
Prior to this weekend I had never played more than 20 minutes of a Diablo game, though according to Steam I've logged about 20 hours on Torchlight, so I'm not really sure whether to qualify myself as a noob to the genre or not...
I am thoroughly, thoroughly impressed with this game. The gameplay is just so ridiculously smooth... it reeks of a refinement that you see in very few games.
I just have nothing bad to say about it whatsoever. My favourite class so far is the Wizard, mainly because of how immensely satisfying it is to evaporate a group of monsters from across the screen with a few lazy bursts of chain lightning.
It's easy to understand the direction WoW has been going recently after seeing how streamlined Diablo III is. Every peripheral feature is secondary to the gameplay itself. Sell and salvage straight from your bag. No talent trees-- just choose the abilities you want at that minute. No equipment binding. Shared professions between characters. Mana regeneration is fast and constant. Skip all the quest text and follow the map arrows.
Just kill monsters, get loot.
I can't believe how fucking short this damn demo is. =|