Not that I'm an experienced fiction author or anything, but usually when I craft stories for publication, it seems I'm exercising different writing muscles compared to when I'm writing for a game.
By a game, I really mean pen-and-paper RPGs. I'm not talking about writing published adventures (which poses different problems on its own) but rather creating and weaving a story for my players when I'm the GM.
I mean when preparing a game, I have to consider an immediate, tangible gratification for my players, whether this might mean a battle, a role-playing opportunity, or a chance to simply "level up".
Second is that I need to leave hooks for my players. I mean unlike in fiction where I more or less have "control" over my characters (relatively speaking--I can't make them act "out of character"), players in general can be quite unpredictable and take your game in unexpected directions (sure, I can railroad the story to where I want to go but where's the fun in that?).
Third, which I think is an important differentiation for "serious" writers, is that I leave originality behind when I'm gaming. That's not to say I don't have original ideas, but if there's a time to pull off cliche lines and scenes, this is the time to do it. Gaming, after all, isn't targeted at a mass audience but rather your small gaming group. You want to draw upon shared experiences, shared cultural knowledge, shared ideals of adventure.
Oh, and when I'm running a D&D game, I have to juggle anywhere from four to six different characters, yet giving each one focus but at the same time emphasizing the group identity as well as that of the individual.
I'm not saying anything new here but rather this is all a prologue for an article at Ars Technica on video game writing, an experience I haven't encountered yet: Creating Characters with Susan O'Connor.