Storyline, of the two, is wht keeps me playing a game.
I hated Final Fantasy 8. It had really good graphics,
but the storyline sucked. My personal favorite was FF6.
I HATE bringing Final Fantasy into this, but it's just an example.
As for gameplay, that's also very important. I'd say it is a dead tie between storyline and gameplay, if not gameplay more, because even if the story is good, if the gameplay sucks, I'm not going to play the game.
That's what confuses me though, WoW does not have the best graphics, and yet it's still so popular.
If people rely on graphics so much, like most people I know do, then why do they play it?
Gameplay, that's just it.