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.