In a Diablo post-mortem at GDC, game designer David Brevik revealed that Blizzard’s famous action RPG was originally pitched as a turn-based game. Planned to be more similar to the step movement, grid-based, turn-based gameplay of Nethack and Rogue, Blizzard’s Diablo was meant to be more of a classic “roguelike” than the streamlined variant it eventually became.
The transition from turn-based rogue clone to real-time action RPG occurred due to publisher’s insistence that, quote, “real-time will be better”. This isn’t too hard to believe, given that the PC RPG genre was considered (by publishers) to be dead during the mid 90s. Amusingly, Diablo is often cited as being one of the titles responsible for its resurgence.
The full .pdf of the original 1994 design document can be viewed online. Fans may find it an interesting read, since according to the document, many of the game’s initial features and story ideas never made it beyond the planning stage. The document also makes mention of an expansion taking place in a “fungus world”, which obviously (and unfortunately) never happened. The only worthwhile expansion to the game, Hellfire, came by way of Sierra On-line in late 1997.