The Diablo: Hellfire expansion is coming to GoG with full permission from Blizzard in a rare nod to the importance of the early, unofficial content beloved by older players. The original Diablo was made available for the first time on digital distribution on GoG's platform only recently, more than twenty years after its initial release.
When Diablo was announced to arrive on GoG, there was no mention of the Hellfire expansion at first. This was due to one simple but important reason: Hellfire was not a Blizzard-developed expansion, nor was it endorsed or properly recognized in any meaningful way for years after its release. Instead, Hellfire was made independently and was well ahead of its time with what it offered players to such a point that Blizzard did not come close to offering anything of comparable scope until its release of the Diablo II expansion, Lord of Destruction.
Developed by Synergistic Software and released in 1997, Hellfire offered a generous amount of content akin to a modern expansion today. It featured a full single-player story, the addition of a new character class, the Monk, new weapons, armor sets, missions, locations, dungeons, and enemies to fight. By comparison, this is roughly the type of content released in the Reaper of Souls expansion for Diablo 3.
The decision by Blizzard may seem like an act of goodwill, however, some speculate that this may simply be setting the stage for a project that fans have been requesting for years: an HD remake of Diablo or Diablo II. In many ways, both are primed to receive the same treatment that Blizzard is giving to Warcraft III: Reforged, as the developer has provided numerous quality of life improvements to both games for years.
Remastering old content does seem like an easy way to both strengthen a franchise by appeasing long-term fans, and extend the amount of time for proper sequels to be released. Diablo 4 is one title that comes to mind, as attendees at BlizzCon 2018 discussed with great anticipation before the event that if the next installment was not announced, they would be more than happy with a remaster of an old title to tide them over. We know now that Blizzard instead revealed Diablo: Immortal, with results that were less than ideal.
The Hellfire expansion is not being sold individually. It is bundled with the original game at no extra cost to the player.
If you are an old-school player, or simply want to experience the hit series from the very beginning, now is a great time to check it out. The game is currently listed with a 10% discount during the GoG Summer Sale Festival which is currently running until June 17th.