Game that I think are influential, important, and impactful to the progression of video games.
I'll try to provide a reason for each game here.
If you have any games that you should be here mention them, preferably with why they should be here.

Games Under Consideration:
-Computer Space (1971)
-Heiankyo Alien (1979)
-Akalabeth: World of Doom (1980)
-Mystery House (1980)
-Tempest (1981)
-M.U.L.E. (1983)
-Archon (1983)
-Hydlide (1984)
-Commando (1985)
-Gauntlet (1985)
-Maniac Mansion (1987)
-Sid Meier's Pirates! (1987)
-Dungeon Master (1987)
-Herzog (1988)
-Herzog Zwei (1989)
-Populous (1989)
-Lemmings (1991)
-Micro Machines (1991)
-Flashback: The Quest for Identity (1992)
-Sam & Max Hit the Road (1993)
-Day of the Tentacle (1993)
-Tokimeki Memorial (1994)
-Command & Conquer: Red Alert (1996)
-Grim Fandango (1998)
-Baldur's Gate (1998)
-Suikoden II (1998)
-Planescape: Torment (1998)