Not world-changing, but I thought Golden Sun was groundbreaking.
Lot of fun, good story, great replayability.
No, wait...
PONG!
Quote: ...Tetris...
/signed
A way a lone a last a loved a long the riverrun, past Eve and Adam's, from swerve of shore to bend of bay,
brings us by a commodius vicus of recirculation back to Howth Castle and Environs.
Tetris is one of the few people have mentioned which I think deserve to be on that list. Many others deserve to be on a different list (games which have changed gaming). I could think up a pretty extensive list of influential FPS games (influential on other FPSs, not on the world). Wolfenstein 3D, Doom, Duke Nukem 3D, Half-Life (and maybe 2), Deus Ex, Thief: The Dark Project (and 2), System Shock (and 2)...