I wish this game actually felt like a sequel to Diablo II instead of its own thing. I just feel like Jay wanted a "clean slate" after the fallout of Blizzard North's collapse. It's a slap in the face to all of the fans and I still have bad blood about it. I know it's their game, but Blizzard lore is legendary in itself.
While I also wish that D3 was more of a direct sequel to D2 (I loved how the Barbarian was supposed to be the same one originally and was disappointed they backed off on that), I'm not really sure Blizzard's lore was ever very legendary for the Diablo series.
Speaking for myself, I never felt particularly attached to "Sanctuary" as a cohesive world, and I never felt like there was much back story but for a few characters (like Tal'Rasha. But, who was Sigon? Trang-Oul?).
That said, I do feel like D3 was a missed opportunity to develop some sound lore, and the reconning the Dark Wanderer was just a shame.
I think that it always had the potential to be legendary, but there was just too much back-filling. It is understandable though, when the original game was created in the 90's, I don't think they had a clue how big it would eventually become. The story and the need for all the back story forced them into all the back-filling and retcons.
I don't necessarily love it or even like it, but as a writer, I can understand that they were forced to write their way out of a corner more than once.
We should expect that there will be yet another expansion after Reaper of Souls, and with that I wondered what the next class or classes could/should be. I know there will be a great deal of clamoring for a return of the necromancer, but I often thought that a class formed by renegade Viz-Jag'taar would be pretty cool.
Something between the D2 Assassin and the D3 Monk would be pretty cool.