Too much watered down.
Too simple, too boring. The only thing I liked so far is the graphics. I am still hopeful that I may eventually start to enjoy it but I won't hold my breath. The thrill and adventure of the previous Diablo episodes are dead. I remember Diablo 1-2 feeling like you were in a horror story. Diablo 3 is a farce.
One can argue that it's still new and players played only a small part of it. To that I say, if you have been playing games for years then you can tell a very easy and simple and boring game after playing 10+ hours.
Don't buy it if you have not done so already. If you want to give it a try, try to find a friend who has it and play his game to make sure you want to buy it before wasting your money.