Diablo is still a great game - it's very, very simplistic in storyline and actual play, but it's still mucho funno. I'm playing through as a Rogue, which means I shoot lots of stuff with lots of arrows, while wearing a chainmail bikini (the Rogue character is female). Funfunfun.
Diablo was one of the first games to devote random-generation to much of the game world. The basic village part of the world never varies, but the 16 primary dungeon levels are always randomly generated. Each block of four (dungeon, catacombs, caves, hell) has its own distinct style and layout rules, making the game, if not unique, then at least varied with each play-through. There are a range of side-quests that do or do-not happen in each play through, so there's a little more variety there (although, you almost invariably face The Butcher on level 2).
Sadly, this play-through-variety is necessary to really enjoy the game, because a) the items available for purchase don't refresh fast enough in a single game and b) more advanced dungeon levels are exponentially more difficult, meaning it's usually necessary to restart the game with a mid-to-high-level character in order to gain sufficient character levels and magical equipment to reliably defeat high-level nasties.
I'm probably going to restart the game, again, once I labouriously clear level 13, because the stupid frickin' Steel Lords are fucking difficult. I can take them one or two at a time, but larger groups are seriously dangerous. I need better armour, and high levels of the Lightning spell, to be able to take them.
I couldn't get Hellfire, the add-on package, working. Searching on-line for help, I stumbled across too many unrelated websites or just plain non-functional shit. If you put "Hellfire" and "cheat" into Google, you get many apocalyptic-christian websites, by which I was informed I would burn forever for cheating, regardless of the type of cheating.