This should be a multiple choice, cause story got my vote, it's what I like in my games most, and it is what pulls me in to keep playing.
But then WHY AM I PLAYING MINECRAFT?
Some games I just get for the coop, others just for the fun, this pool would have way more accuracy if the vote would be on the LEAST important part of the game. Cause good coop games don't even need much of a story, cause you're having fun with friends, make one up as you go, you're not alone. But if I am alone, then it's all about the story.