InfiniteClouds: I played Diablo 2 first... before playing this game for the first time many years back... and while I was glad it spawned the sequel because D2 was a great experience I never understood why Diablo was so successful. I didn't really get into PC gaming until about '98 but I have gone back and played many games from throughout the 90s and compared to the other offerings available all throughout 1996 it surprised me that it was met with such praise.
One town.
One dungeon.
Three classes.
If I was a PC gamer at the time I would definitely have been too busy with Elder Scrolls II to bother with this game. Even going back some years before many CRPGs offered much more than this
Might and Magic: World of Xeen, Ultima VII, Menzoberranzan, Ravenloft, the Ultima Underworld series, etc.
That said, I loved Diablo 2 -- the exploration, skill trees (both totally absent in Diablo), and story (contrasted to most of Diablo's being contained in its manual) was all great fun.
A fair question.
Diablo (one) is one of the first games I played which TOTALLY IMMERSED me. I was a much younger man at the time... and it was a game which resulted in a fair number of literally sleepless nights, where I started playing, intending to play for a couple of hours before going to bed, and was broken out of my game-playing reverie by my alarm clock going off. I literally played through the night, more than once, with no sense of "real time" passing.
Now, for me, I played SINGLE PLAYER only. I tried a couple of co-op games, but never really enjoyed being at the mercy of others... even if (as was the case here) they were people I already knew. Having to wait for someone to get started... hearing their kids yelling in the background on the conference call we'd share... etc... broke the immersion factor for me.
But... playing alone... total immersion. Forgetting the world around me. And this was the FIRST GAME, EVER to draw me in like this. There have since been a couple of others... "Thief - The Dark Project" comes immediately to mind... or the original Deus Ex... but such quality is pretty rare.
And that's why people loved it as much as they did. Sure, online play may have been a big deal too, but I never met anyone personally who was that into the online side of things. Blizzard loved it and promoted it for later games, and thus the later games (to ME) are LESS IMMERSIVE. The idea that if I need to leave for a minute... to go to the bathroom, answer the door, etc, I either have to let the world go on without me (back in camp) or I have to restart a level which repopulates, with all my progress lost... deeply hurt the "immersion" factor.
Walking back up to a staircase, through levels I beat days ago, walking over the dead bodies of monsters I killed, to get back to the next staircase to the surface... with all that CONSISTENT... it's a big deal. I'd also stockpile weapons I wanted to keep, piles of gold, etc, on the ground around Tristram, and they'd still be there even if I came back weeks later to play more. Diablo II, by contrast... unless you have it in your pack or in your chest, it's lost, and all the monsters except "quest monsters" have come back again, as if you'd never been there.
Yes, Diablo II allows you to just replay a level over and over until it's too easy to keep playing, then move along. It allows you to boost your states in ways that Diablo I never allowed. In Diablo I, you had only as much experience as you could gain from the levels you'd played as you went to the lower level. You could not gain further experience and stats by spending time re-killing weaker enemies at higher (or is that lower) levels in the game's progression.
You know, as you go in to face the Archbishop Lazarus that you're BARELY strong enough to survive that encounter... if you're not very, very careful, you will be overwhelmed. Period. And when you go to meet Diablo... well... you have to think your actions through very seriously.
In the later games, people breeze right past the "bosses" in too many cases by just "leveling up" beforehand. The first game gave you no such option... and that made it a LOT more challenging, IMHO.
In reality, Diablo and Diablo II are two very, very different games which just happen to look similar. Diablo I is a horror game, where you are challenged to even survive, much less triumph. Diablo II is more of an "action slasher" game... where, if you play well, manage y our rune-words and the like, trade jewels and rare items in the stores, etc, properly, you can beat any foe without breaking a sweat.
I prefer the first game. Many others prefer the second. You have to judge for yourself. But for me, it was the most immersive single-player game I'd ever played at that point, and remains one of my top six favorite games ever.