I played the closed (and open, but they were the same) beta, and the game is great.
Diablo is the KING of this genre of game, so it's the best you can possibly get in this genre. Diablo 3 is officially the most pre-ordered PC game of all time from Amazon, and the most pre-ordered Blizzard game of all time, that includes WoW and its expansions. That tells you something.
"You lack the requisite spine and testicular fortitude to study under me"