For those who are interested, Blizzard is running an Open Beta of Diablo 3 this weekend. I've played through the Beta (which is just Act 1) with the Monk, and will try the other classes.
So far, I'm...underwhelmed. It's not bad, but compared to what I was hoping for, it is lacking. I never came close to dying, and only had to use healing potions on a few bosses. (I wasn't using the Monk's healing ability, either.) There was really no need to swap powers. I chose two attacks and kept them through the entire Act. (More unlocked, but I just didn't see the need in swapping out what I had.) There are no side quests. Cap for the Beta is 13, but I beat it at 9. You can go back and replay parts of the questline, but it's just to grind. (I replayed the last part and got my Monk up to almost-11.)
I was all set to pre-order the game, but now I am not sure. I will get it eventually, but am in no hurry.