Diablo is pretty much the original action RPG, with randomly a generated dungeon, hunt and fetch quests, random loot drops, class based skill trees and equipment sets, etc. The original and Diablo 2 (with its expansion) have sold a million billion copies, and since their release a decade ago or more ago have been in the top 10 monthly sales charts for PC games.
Diablo is kind of like Aleroth in Divine Divinity (town and dungeon), if you take away most of the humour, dialog and quests, world interaction, make the catacombs 15 or whatever levels deep and randomly generated, and get limited inventory slots and scrolls of town portals rather than teleporter stones, and throw in respawning opponents. Diablo 2 added more classes, etc, and much more area above ground (different locations), still with various randomly generated dungeons.
There is a mod for Never Winter Nights re-creating the original Diablo.
