The interesting thing to me is D3 had everything going for it before it was developed and released. It had an answer book with D2's success. They had a rabid fan base with over 10 years of data to see what did and didn't work with D2.

To be fair I only played D2 in 1.09, 1.10 and 1.12 with LoD so I don't know what day 1 looked like but I'd consider D2 still to this day the best ARPG I ever played where as I stopped playing D3 shortly after release after completing it (before it nerfed everything) in hardcore mode from the beginning, it had no longevity. I didn't even buy D4.

I think it's harder to have a sequel be well received when the previous version was considered as good as it gets for a large player base. With that said, I'm still surprised how D3 panned out.