D3 wasn't a failure by anyone's standards. It sold like what, 30 million copies with the expansions combined? D2 only sold 4 million to date. D3 WAS fun. i loved it when it first came out. But i played D2 for 5-6 years before getting bored, i only played D3 for barley 5-6 months before becoming much more bored than i was of D2, i even went back to D2 for a little bit. D3 just didn't have the same community feel as D2 had. And with the lack of pvp, a lot of people bought it, but quit shortly after. We came back for the expansion, but again, for only a few months. And seasons? less than 2 weeks into each season until its boring again.
I have a lot higher hopes for D4 based on what we've seen. Back to the D2 feel, with major improvements. I had no complaints about wanting D3 to make me feel 12 or be completely blown away again. I had specific complaints like the soft/glowy graphics, end-game content, how crafting/trading worked, no pvp ect. But i agree D3 was/is a great game and anyone calling it a failure is just butthurt.