Myst is legend. But pretty hard with all that brainteasing. Especially Uru - Path of the Shell.
I guess you've already checked out the old C&C games. What about:
Space Colony. Metal Fatigue. Legacy of Kain (Soul Reaver). Revenant. Age of Mythology. Throne of Darkness. Age of Empires 1. System Shock. Galactic Battlegrounds. Star Control. Serious Sam. Heaven&Hell. Oni. American Mgee's Alice. Unreal. Heroes of Might&Magic. Grim Fandango. Robin Hood (Legend of Sherwood). Scrapland. Gunmetal. Swine. Aquanox. Flying Heroes. Mechwarrior. Knights and Merchants. Kiss: Psycho Circus. Battlezone. Gangsters. Warlords Battlecry. Indiana Jones. Battle Realms. Starcraft. Warcraft. Alien vs Predator. Restricted Area. Starsiege. Wheel of Time.
While you dont seem to put a genre behind each game so I know whats worth checking out, over half ive played. Some I heard about, some I deleted, some I will never play.