I think Diablo 3 is probably fine if you've never played a Diablo game before but I know very few people who liked the previous games who were happy with it.
The skill system revamp was a big let down and everything is generally too dumbed down and homogenous. The loot doesn't even set you apart thanks to the AH. They also failed on the social front, chat channels are a great community builder that should have been in the game from the beginning. Once your friends stop playing there is this total sense of isolation, there could be 20 or 20,000,000 people playing Diablo 3 and you have no idea. The only indicator of activity is the games stupid auction house.
Speaking of the auction house, total failure on every front. I don't care if people traded on third party websites in Diablo 2, putting that functionality into the game ruins one of its major core concepts. The idea that they didn't balance around is laughable.