I think it still is, especially if you have friends to play it with. With all the vitriol with regards to Inferno being a grind-fest in order to progress, I do think it is a more of a thinking game compared to Diablo 2, with classes being able to adopt roles in a group with ease. The higher difficulties (especially true with Inferno) are much more fun in a group setting and there's a lot of strategy involved in coordinating roles and load-outs between your party members. There's a whole lot of strategy involved than most people think.
It is actually fun from 1 to 60 if you avoid the AH (though near the end of Hell you might need to). Replayability is totally down from Diablo 2 though.
I found your other post to focus on the wrong aspects of D3, but this one is right on.
It's pretty fun 1-60, especially with a friend.
As soon as you play a bit longer you quickly realize that most people just quit trying to loot in regular intervals to use the AH. They only pick up gear to sell to merchants.
Before I was even hacked I realized the replayability wasn't there and donated for a beta invite to Path of Exile.
Yeah, I think D3 nailed the social aspect of leveling. I only had one friend playing the game, but I ended playing regularly with over 10 other people that I just met in game randomly.