In System Wars, I always hear people stating that gameplay is more important than everything else that makes up a video game.
Video games are works of art. All aspects should be great in a great game.
If Uncharted 2 had horrible visuals, then the game's overall quality would not be the same, but that doesn't mean the gameplay was by any means bad.
If one aspect of a game is sub-par, the rest of the game goes with it. Gran Turismo 5 is a prime example of that.
The overall design of a game can easily render the graphics and/or story useless. I believe this is where the argument originated from. Many Nintendo games are designed so well, they don't need graphics or a story in order to be great. Keep in mind that it's not JUST the gameplay that makes these games good. It's the overall design.
Great gameplay alone makes a shallow game. You need a good design to make it into something more.