If I could nominate a body of games, perhaps Geller's King's Indians in the Zurich 1953 Candidates Tournament. Bronstein, as I recall, said that Geller showed them all the way to play the KID at that time.
That's the best I can do--Just repeat what seems the important and sensible opinion of a genuine player.
To goldendog
Good choice; Geller (along with Bronstein) showed the world the KID. BTW, I don't live in beertopia as you do, but I visit any chance I get.
In a similar vein, the Kasparov/Kramnik world championship match, where Kramnik brought out the Berlin Wall. It seems to have virtually put paid to 1. e4 among top-flight grandmasters
I'd say the most important theoretical game would be one between Winston Churchill and Adolf Hitler on September 1st 1939 upon the result of which the outcome of the second world war would be determined and immediately enacted.
To NickYoung5
Good point, and one I had not considered (though I'm playing the Scotch Gambit now because of it).
Marshall-capablanca, the one with the Marshall Attack
If you mean Capablanca-Marshall, 1918, then I agree, it certainly deserves mention as one of the most important and famous novelties of all time.
that's the one, Marshall lost though:
I was wondering what other players consider to be the most theoretically important game in chess history. My vote is for Pillsbury-Tarrasch, Hastings 1895, the game that made Queen's Gambit famous. Until then, the QGD was considered bad for white--once black played c4, all endings favored him. Pillsbury showed the attacking chances for white, and the rest, as they say, is history. What's your choice for most important theoretical game?