LOCUS says so, so it must be true. They did their once-every-decade-or-so megapoll for the Best Science Fiction and Fantasy of All Time, and A GAME OF THRONES finished in the second place for the Best Fantasy Novel of the twentieth century, behind this guy named Tolkien. Tolkien was third as well, followed by Le Guin and Zelazny. You don't get into more rarified company than that.
(A STORM OF SWORDS and A CLASH OF KINGS showed up on the 20th century poll as well, further down).
I even made the Best Fantasy Novel of the Twenty-FIRST century top five, with A FEAST FOR CROWS in fifth.
((Actually, I tend to think that at least some of the people who voted for A GAME OF THRONES were voting for the entire series. Makes more sense that way. You will note that Tolkien's first place winner was LORD OF THE RINGS... they did not divide his novel into its three component volumes, but mine did get sliced into five separate entries, maybe because its unfinished as of yet.
Anyway... you have to take these kind of polls with a whole shaker of salt, but still, it's cool. Thanks to everyone who voted for me.
You can peruse the full results here:
(FWIW, Frank Herbert's DUNE finished first in SF and ENDER'S GAME was second, but my own top three would have been LORD OF LIGHT (Zelazny), THE STARS MY DESTINATION (Bester), and THE LEFT HAND OF DARKNESS (Le Guin).