I don't know if I can put into percentages, but it all requires a healthy balance.
I think all games should look good. That doesn't mean graphics, mind you; we're talking purely aesthetics (A good example: Parappa the Rapper's art style helps the game look nice and fresh today, even though it was made for the PS1. Gears of War, despite benefiting from the graphical power of the 360, has an ugly, dull, and forgettable design). They draw a player into the world of the game, immersing them in the whole experience.
Story is key for me. I've found that when I get drawn into the tale a game weaves, I can easily forgive (or just not notice) many minor flaws when it comes to gameplay. A good example, for me anyway, is Grand Theft Auto IV. Many people have told me that the gameplay was stiff and boring; they may be right, but I was so interested in Niko Bellic's story that I never had those issues.
Finally, there's the gameplay. It's kind of like the skeleton; if you don't have a strong backbone of gameplay, the whole structure is going to collapse into a mushy blob. It isn't everything, but it can't be neglected either. If it isn't engaging and enjoyable, at least on some level, than no amount of storytelling prowess or aesthetic brilliance can salvage the game.
Now, there are exceptions, but this is just a general list of the necessary components to construct a good videogame.