Gameplay, graphics only outweigh gameplay in certain situations..
I have played games with great graphics, but were just not fun to play, and games with subpar graphics but keep me entertained. Marvel v.s Capcom is a 2d sprite fighter and I still think that's more fun than Dead or Alive on the 360. Graphics look great in screenshots and cutscenes, but when you have the game for a week, you don't want to be bored already.
Gameplay is the foundation of a good game, graphics are just the icing (even though it is necessary icing).