http://www.blizzard.com/diablo3/
For me Diablo 2 was the best hack'n'slash game ever when it was released (and of course Diablo 1 <- a classic and it is the best too

and even after D2 was released - it remain to be the best. As far as I remember all games which were hack'n'slash and released after D2 - they just didn't make it. Diablo 2 was the best until now I guess.
The gameplay trailer which you can see - presents Barbarian Class, Witch Doctor - overall game improvements, beautiful fully 3D graphics and most important thing and addition in Diablo III - new physics system with destructible environment.
To be honest the game looks big, the trailer is long and it made my day, lol. I will definately buy this game.