It’s playable for free, although you’re limited to the demo version with one character class, a fraction of the levels and virtually none of the conversations with Tristram’s residents. Don’t fret, though. If you have a copy of the full game (whether from GOG, a disc or elsewhere), you can load its main data file and play all the way through to the climactic battle with Diablo himself. Whichever version you play, it’s a way to both trace the roots of the Diablo series and see how much the genre has evolved in 23 years.