Left 4 dead 2 is not a game to play for story, because we all know it sucks when you play it on single player, it like most of Valve's game's are all about the multiplayer, and i have no clue why anyone would buy L4D2 for an epic story, the main focus on the game is multiplayer, always been.
Sometimes i love to play games with great stories, but a game with great multiplayer such as Unreal tournament, does not need a story at all.
RPG's? need great stories, because more than often it will be a single player long experience, and if it has no story, it has no appeal, no multiplayer to back it up, so story is all it has.
2010 a great year for 360!