Hey! Remember Diablo? Blizzard sure does, and it's currently celebrating the game's 20th anniversary (it debuted on the final day of '96) with a special Diablo III in-game event this month that recreates key aspects of the original game.
Most notably, as part of the "Darkening of Tristram" event Diablo's centerpiece 16-level dungeon will be recreated in Diablo III, affording contemporary players and devs an interesting perspective on the original game's design.
According to a promo video for the event, which went live this week in Diablo III patch 2.4.3, the optional retrograde encompasses original Diablo levels and bosses but also includes changes to Diablo III's camera, audio, and user interface that evoke the original game.
Blizzard has said it plans to revive this Diablo promo in Diablo III every year to celebrate the original game's birthday, and it's making an effort to promote the seminal action-RPG in a number of other ways -- including sharing a fun retrospective video featuring Blizzard devs that we've taken the liberty of embedding above.
For more on how the game came to be and how it changed from concept (as a turn-based isometric RPG!) to completion, check out designer David Brevik's recent postmortem of the project and the original Diablo pitch document he submitted in 1994.