[talloaktrees]

at the time when Diablo came out it was clear it was a polished, graphical version of Nethack

[ido]

It was more like a polished graphical off-shot of Angband. But I wouldn't call it a "version of it" anymore than I'd call Battlefield a version of Doom (or any platformer a version of Super Mario), they are simply games in the same (or similar) genre.