I didn't play D2 or D1, and I still think D3 will be a great game, so I'd have to 2nd what these two guys already said.
I've been in the beta for awhile, and it's a really good game that looks like it will have a lot of replay-ability to me. All the classes have unique but great skills and that makes me want to try all of them.
One thing blizz brings to the table is, around 7-8 years of dealing with the worlds top MMO, so they do know a thing or 2 when it comes making RPG games. And they also have their past games they've done as well, W1,2,3, SC1,2, D1,2, and well 3.
I'm sure Blizzard has NO IDEA of how to make a good game... lol