I got a chance to play it and here are my thoughts on it.
The best way to put is, Diablo 3 doesn't feel like a Diablo game. I agree the core elements are there, but what made Diablo 1 & 2 great was 1: music, 2: a definitive art style, 3: cut scenes and 4: random dungeons and out side of town. None of these criteria were met in a satisfactory manor, and here is my opinion as to why it fails (on the points mentioned before):
1: The music was mainly background and didn't engrose me into the game. There was NOTHING that made the games music stand out what so ever.
2: The art is just WoW 2.0. If you don't agree then you're not paying attention to what the previous games were and you're love for WoW is clouding your judgement. Also, it's nice to see the armor change but when I put on fucking plate-mail it should be plate-mail, not something different. This was right in the other games, why is it lacking now?!?
3: There were ZERO cutscenes, everything was done in game, much like diablo 1 & 2 I'll grant you, but NOTHING?!? This is what made Diablo 2 feel so damn epic, why is it GONE?!?
4: To be fair, I only got to play the first area which might just be prefab with some shallow random placements of where you can go for an encounter, but why is anything static?!? Honestly, this was a DEFINING feature in Diablo 1 & 2 even from the start area, what the hell is wrong with Blizzard?!?
The art also brings up another problem I for-see, if the game changes the art based on tiered gear, this hints at the fact the game will not have gear that looks different. I am not saying this is the case, but since I know of no one who has played past the first chapter, I am raising the "whoa wait a minute flag".
This is not the Diablo game fans were expecting and for Blizzard to do what they have almost borders on the cruel, they sold out, to make the game easy for every one and think we all need to have simple experience. This is for those who whine about Super Mario Bro's being too tough, well do me a favor ass holes, SUCK IT UP! Not everything is going to be easy and the fact game dev's are giving you this shit on a platter, pisses me off because it's ruining the game franchise's I use to love!