I think one of the things I really enjoy about Joy Division is that Ian Curtis brought the band "artistic discipline". I most often find myself listening to the music not for "doom and gloom" or something "Gothic", but for the pleasure of feeling someone driven by the integrity which has always produced great art.
Most artists seem driven by money or fame, or at least heavily influenced by it. They're pressured to release songs on a schedule, so as to satisfy journalists or safeguard their revenue stream. Or they worry that their new release is not in the Top Ten, so that consequently they're not "respected", and so they throw away their personal vision and make something that sounds like whatever's trendy.
Joy Division never subscribed to that. Perhaps they could only maintain their output for about a year-and-a-half (1979 to mid-1980), but for that time they set a very high standard. No release was crap, no B-side was a studio throw-away. And both albums have consistently great songs - if the song isn't great on the album, it's likely (if not certainly) great live.
Nothing Joy Division produced was for the money. Singles and albums did not appear in multiple versions with different covers, and singles were artistic statements separate from the albums themselves. (This is contrary to the regular practice of taking a song from an album and turning it into a single.)
And I don't think Ian Curtis was in it for any fame. His lyrics and stage antics were nothing "respectable people" would want to associate with, but he kept on with it all. In the Radio Blackburn interview he complains of journalists, "they like to get you boxed in, saying this group belongs to this category, and this group belongs to this category..." And then: "I don't think we belong to any category. ... We're four people who are playing the kind of music we want to play."
This is the reason Joy Division, twenty years after the loss of its lead singer and its subsequent breakup, still retains its artistic power and cult following. They knew music could well be something worth living and dying for, that music was not just some trivial pastime of boys in a garage or people who didn't take to regular jobs. (Bernard Sumner's claim that he didn't want a regular job may well be the reason New Order is not, in my assessment, timeless.)
Perhaps the most difficult thing that Joy Division faced, and still faces today, is a popular music scene obsessed with money and respect. To ignore such things, to view art as a completely different animal than making money or impressing the neighbors, to be willing to go to the extremes and sacrifice everything for the sake of one's vision - that is precisely the mark of greatness, and that's why, and how, Joy Division achieved immortality.