I was sadly surprised to see that there aren't that many votes for some of my never-completed-yet-on-a-must-do-so-before-dying list, such as:
*Betrayal at Krondor: Terrific semi-open RPG. It probably looks quite pixelated for today's standards, but despite the lack of background music while traveling, it really gives some special 'vibe' with unique atmospheric sounds. The combat style is interesting and different to other titles. As others, I hit that game-breaking bug, so had to drop it before the fix was released. But I would definitively love to give it another go. Even the name feels 'right'. Never tried Betrayal at Antara, though.
*Mechwarrior 2:Mercenaries / Heavy Gear - Later titles never reached the same level than Mercs. Actually, I rather much prefer a proper new installment of either. I did finish MC2:Mercenaries but it deserves another run.
*The Elder Scrolls: Daggerfall - I tried the free Arena sometime ago, and the initial dungeon was fun, but after reaching the town, it looked as those games that would take some time to complete, so I postponed it for the future. Daggerfall is even larger (by a great margin), but I like the background story more, so if I have to pour many hours on a game, it better be one that has the King of Worms and Barenziah as central characters...
Would also like to get Redguard and Battlespire.
*Syndicate - "It's in your head", that's enough of a reason. (All Bullfrog titles, actually)
*Drakkan: The Order of Flame - I'm surprised that there weren't more sequels or copycats in the PC at time. The game is really visually rich, and fun to play (despite some restrictions with controllers) and I suspect it has aged well enough.
*ONi - The only game (aside of Bloodlines and Fallout) I have felt the need to complete more than once. They really nailed the control scheme, and the game is truly fun. It's basically "Ghost in the Shell" on the West, and pretty darn good on that.
*All the Westwood Studios games: With "Eye of the Beholder", "Lands of Lore", "Command&Conquer" series, plus "Blade Runner" and "Legend of Kyrandia" in the catalogue, you can't go wrong..
*Alone in the Dark 1&2: The precursor of the survival horror theme. In pseudo 3D, in a time where those techniques were used more in Simulators. Still remember that moment at the beginning of the game, with the window and all... It also has one of my fondest gaming memories when was young: I remember having heard mother calling me for dinner at some point. Later, when I finally managed to exit the mansion with a huge sense of accomplishment, noticed the faint rays of sun percolating in my room.. Completely immersed in the game, never noticed that a full night have came and gone.
*One must Fall - The original, not the horrendous OMF:Battlegrounds.
One of PC's finest Beat'em ups. With Robots and stats. It's OMF.
*Gabriel Knight series. Sierra On-Line obviously has a lot of games (adventures + Star War), but such series never got the mainstream exposition that it deserves.
*Flashback, Fade to Black - semi sequels to "Another World". Flashback is still good looking. (Not sure if it was ever released on XBOX live or Steam, but I don't use those services anyway)
And I never managed to play any of these, but picked my interest nonetheless:
*Wizardry, Ultima and Realms of Arkania series, Veil of Darkness, Dark Seed, Dark sun, Albion.. all RPGs.
We really need more good RPGs here, specially the less known ones.