There was (hopefully still is) a thriving community of D2 single player enthusiasts that had a very welcoming crowd and managed to avoid the craziness of battle.net[1] at the Single Player Forum of diabloii.net[2]. To this day, it's maybe my ideal of the internet done right (though its in-page ads seem a little more obnoxious now than I remember).
It had fairly strict rules w.r.t. documenting what mods you play with[3] but most folks used certain baseline tools such as infinite stashes[4] that greatly helped with playability.
The pace in single player is significantly slower without overpowered items, but also significantly more tactical. And there were often seemingly absurd self-imposed constraints imposed to make gameplay harder on yourself (no uniques, etc.). Here's one player who made it through hardcore in all difficulties (Guardian) doing full clears with a naked Amazon[5].
While not as extreme, and maybe it'd be insignificant on battle.net, I had some of my most satisfying D2 moments there[6].
[1] Good luck getting enigma and other overpowered runewords in single player.
[2] https://www.diabloii.net/forums/forums/single-player-forum.3...
[3] There was a vibrant trading scene but this helped discourage cross-contamination between, say, a vanilla player's items and those of a player who enabled ladder-only runewords.
[4] GoMule and ATMA may have been my first exposure to Java programs.
[5] https://www.diabloii.net/forums/threads/how-far-can-superdav...
[6] https://www.diabloii.net/forums/threads/finally-my-first-gua...