QWEEDDYZ: But mods\remakes =\= original game. It always only alternative.

vv221: DevilutionX is not a mod. Nor a remake.
It is a new engine for Diablo, a new implementation providing the vanilla experience on modern systems.

You could compare it to OpenMW for Morrowind or Julius for Cæsar Ⅲ.

advowson: Multiplayer mode, whether alone or with others, is more popular with people who wanted to get the most out of the game.

Single player also has the New Game option, which works mostly the same. However, in single player, the deeper areas are only opened once you have reached them normally, so you must fight your way through the early floors again even if you only want to see the deep floors. Most people don't like that, which is why multiplayer is preferred.

Note that multiplayer has even less story than single player. There are only 4 quests, and they are always enabled: The Butcher (floor 2), The Skeleton King (floor 3, randomly placed; unlike SP, where this takes place in a special mini-level), The Vile Betrayer (floor 15, fixed location; not on a mini-level), and Diablo (floor 16; whole floor's layout is fixed).