Eye of the Beholder 1 and 3 are okay, but EOB2 is where it's at, and if you're not sure you want to power through an entire trilogy of decades-old dungeon crawling it works perfectly well as a standalone experience. It's got everything a great D&D game needs, including sprawling dungeons, sinister bad guys, and a clean, clear divide between good and evil.
It's also really tough, so be prepared: Build a hard-hitting party, jack all your character stats to the max, and be sure to save the game just before you enter the Drow dungeon and do not—do not—overwrite it. Trust me on this.
The Eye of the Beholder trilogy is free on GOG in order to draw your attention to the D&D games sale that kicked off today, with discounts of up to 75 percent on standalone games and collections including obscure stuff like Al-Qadim: The Genie's Curse, the Troika-developed 2003 Greyhawk game Temple of Elemental Evil (which isn't great but has a wonderful soundtrack), and Beamdog's Enhanced Editions of Baldur's Gate, Icewind Dale, Planescape Torment, and Neverwinter Nights.
The sale comes ahead of the start of D&D Live 2020: Roll w/ Advantage, a two-day Wizards of the Coast livestream raising money for the Red Nose Day charity to help children impacted by the COVID-19 pandemic.
GOG's D&D sale runs until June 25, but the Eye of the Beholder 2 giveaway is only available until 1 pm ET on June 19.