Before you start worrying about the aesthetics and awesome graphics of your game, you need to develop a story. This is absolutely crucial in some games, such as fantasy RPG games. In other games, such as sports games, there is almost no story required. However, in most games, a story adds a great deal to your game.
So you’re running around some island shooting terrorists in some realistic looking FPS game, but why? There needs to be a story. Play a few popular games. Most of them will have some kind of story. Even apps like Angry Birds and Cut the Rope have a little cutscene before the game begins.
Imagine if you opened Angry Birds for the first time and started level one. Then immediately you were given a few red birds and a slingshot and a bunch of green pigs to kill. That would be weird. You would be wondering, what do these birds have against pigs? Without a story, you’d never know. You would think that maybe these birds happen to be bacon lovers. Or maybe they don’t like things that snort. But no, we know that the pigs stole the birds’ precious eggs. Kidnapping. Or birdnapping. Anyway. Story adds reason. It lets the gamer know who the good guys are, who the bad guys are, and why. You don’t need to make hundreds of complex cutscene animations and character dialog, but you need something. So, yeah. Important stuff.