Oh boy. There's been lots. Alas, my perspective is PC centric, although I know about the Marios and the Zeldas and the what nots.
RPGS - Ultima and Wizardry are the seminal classics of the genre. Do you play RPGS? The RPGS you are playing were heavily influenced by one or both of these games. Ultima pushed elaborately detailed open worlds, NPC schedules, and thematic/plot rich stories. Wizardry was more on the "big party, tactical dungeon crawl" side of things. The Elder Scrolls is basically Ultima's spiritual successor, although it's still struggling to catch up on the thematic depth. Wizardry's impact hasn't been felt as much lately, although it was strong in the late 80's and through the 90's. Series like Bard's Tale, Wasteland, Might and Magic, Dungeon Master, etc were all PURE Wizardry. The only recent entrant in that genre is deliberate throwback Legend of Grimrock, although you could argue that the FPS/dungeon crawl hybrid that came up via Ultima Underworld owed much to Wizardry.
Later highly influential RPGS: Baldur's Gate 2, Planescape Torment, Diablo
FPS - Doom and Half Life 2. You could argue Wolfenstein over Doom, but Doom felt more like the watershed moment. And almost every FPS post Half Life 2 has been HEAVILY informed by its design.
The FPS is a relatively new genre, although some of the later heavily hybridized games are becoming influential in their own right, most specifically System Shock 2 (which birthed the Bioshocks and arguably Dead Space as well) and Deus Ex.
STRATEGY - I want to say XCOM, but other than Jagged Alliance and Jagged Alliance 2 and Silent Storm and its own eventual remake...yeah okay XCOM. Also Civilization. Really though the great grandaddy of strategy games is like...M.U.L.E. Will Wright even taps it as his most influential game of all time. You could even toss in "The Ancient Art of War" for RTS buffs, although the high watermark of that genre remains Starcraft.
MMOS - For basic game play modeling and design, Everquest remains the single most influential MMO ever made. For UI design, visual style, and supplementary game play elements WoW is the kingpin of the genre and has been ceaselessly aped. Together they are basically the alpha and omega of MMO design and their respective runaway successes are 95% responsible for the stagnation of the MMORPG genre.
ADVENTURE - People are STILL basically doing King's Quest, just with progressively newer hats.
stormeris said:
So the game isn't really influential then
Only very recently. You could argue MOTB was influenced by Planescape, but as it was largely made by the same people I think you were just seeing their particular stamp carried forward. Now, though, we have a legion of kickstarted RPGs all promising to be the next Planescape, so its influence is finally being felt.