Diablo III offers impressive graphics, and tons of interaction with the enviroment.
You can smash walls, barrels, drop chandeliers, and tons of other enviromental hazards on the unsuspecting hordes.
Enviroments vary wildly, but each one is very nicely done.
With the ability to switch skills in between combats, you can adjust for each new challenge, or if playing with others, to fill different roles.
Blizzard is also trying to keep up with class balance, making sure one class style/choice doesn't far outweigh any other.
It's an ongoing process, but Blizzard is keeping an eye on this, and this will matter once PvP is implemented in a future patch.
With Diablo III, Blizzard has begun to use a DRM that requires you to have internet connection.
If you lose, or don't have internet, you can't play.
Blizzards servers have also been overloaded, seemingly unprepared for the number of people who have chosen to play.
There's also no risk vs reward. Champion and Rare mobs return from D2, and get more difficult as you complete each of the four difficulties, but the loot is the same as any other mob in that area, regardless if it's the toughest, or easiest, to defeat.
The Auction House is also a cause of some concern.
Included worry is in the RMAH, which has been pushed back to mid-June. This feature was originally dated for May 20th.
The unfortunate truth is, right now, the game is not worth the money you would pay for it. With future patches/adjustments/additional bandwidth, and more stabilized servers, the game may be worth the amount you will end up paying for it.