Gameplay... it's a game. People still enjoy Tetris after all and Space Invaders and all manner of clever old games that don't look necessarily fantastic but are still addictive and fun because of the mechanics and challenge.
Graphics are like... the cover of a book. It should look nice, and reflect the quality of the product inside, but if you open a book up and it's crap, you're not going back to it no matter how nice the presentation is.