Depends on the game and genre, but in general I expect good and fun gameplay. I can live with a game with a bad story (or no story at all) but not with a bad gameplay.
But to make an amazing game you need all things to be good: gameplay, story, sound, art style, etc. If you can make all those things good then you have yourself a great game, and most of my favorite games of all time fall into this category. And like I mentioned before out of those things the only thing that I can't stand is bad gameplay, but if the gameplay is good and the other aspects are just "meh" then the game will just be average for me.
There's only one exception I can think of which is 999, the game has a meh gameplay but the story is so freaking amazing that it really doesn't matter, although that might be because you spend 90% of the game reading and not actually playing, which in the end makes the game more like reading a book than playing a game.
Nintendo and PC gamer
