I'm also curious as to how they will treat the interaction with Inarius; does she still love him, despite him twice banishing her? Does she think x eons of torture isn't enough? I'm almost certain we will be tasked with breaking him free from his prison, probably asked by Tyrael so he can help us stave off whatever Lilith is cooking up, but perhaps Inarius won't be charitable about it, I mean, he's been tortured for some 3K years or so, I'd hope the interaction is more interesting than "Thanks hero, have any snacks?"
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If you played the demo, you'd be more inclined to feel it is original art, or at the least, it is D3 models that are built in a new engine; there is a sharpness and quality to the graphics that is far past what D3 has to offer, and D3 is beautiful in its own right. I'm not a graphic artist or well versed on the tech, so I could be wrong, just saying it felt new.
That said, I doubt we'll see it any earlier than winter 2021, and that is my optimism speaking.