Diablo 3 is a good game with alot to recommend it. It wasn't ideal at launch, but they've worked out the kinks and it's still fun to pick up and play.

I think the problem is that Diablo at launch was a test bed for some of their other properties so it ended up with some bad ideas. The RMAH (for example) was a bad idea, but it helped to point them to the right direction in their F2P and other monitizing approaches. The way they handle auto-generated maps and monsters is used quite a bit in the changes they've made to WoW as well as some of their talent choices.

I think for alot of hard core RPG fans, Elder Scrolls and other similar titles do a better job of hitting the sweet spot as they support alot more long term character growth and have a bigger world. But Diablo 3 is still great for people who want to just beat up some pixels and enjoy a little gothic storytelling.