Ironically what got me into Diablo was my then-girlfriend now-spouse insisting that I go back to Diablo 1 with her and experience it for the story, and damn if that didn't hook me quick. Endgame D2 and D3 are great and all, but what makes something great even greater is having any sort of emotional connection to the story the game takes place in.
Also hot damn the ambiance of D1 is just something else.