So, Diablo turns 20. Way to make a gamer feel old, Blizzard.
In the development of the role-playing game as a viable commercial product, this is a very important milestone to mark and celebrate. When Blizzard released Diablo lo those many years ago--as they are quick to remind you--the RPGs-are-dead meme was all over the gaming press (and, as we know now, they weren't paragons of competency- nevermind integrity). It was this game, as part of a wave of RPGs on PC and consoles released at this time, that killed the meme dead and cemented the RPG as a pillar of gaming beyond the tabletop.
(Useless Fact: When it came time to release Dungeons & Dragons's 3rd Edition in 2000, the mastermind behind it--Ryan S. Dancey--would cite Diablo as a key influence in its development saying (paraphrased) that Diablo encapsulated D&D's "core story": explore dungeons, fight monsters, get treasure, power up.)
And if you are at all a regular on Steam, GOG, etc. then you know all about the many isometric-based RPGs made in the wake of Diablo. (Just nabbed a few more in the recently-concluded Steam Winter Sale, and Path of Exile remains a quality free-to-play clone of that game.) The Torchlight games are notable for being made by former Diablo developers, the Divinity series has a notable fandom, and more examples just on Steam alone show that the legacy of Diablo 20 years on is far from faded. (Just look at Pillars of Eternity and Tyranny.)
And now, as Diablo III begins its slow wind-down as the company's isometric RPG offering, we should be watching out for a fourth game in this series- maybe even announced this year (and this year would be a good time to do so). Congratulations to you, Diablo, for without you the RPGs of today would be in a much sadder state- and one utterly dominated by Japan (because this is also the 20th anniversary of Final Fantasy VII).