With games, more so than perhaps any other medium, it isn't the destination that counts it's the journey. Books and movies are ruled by the way they conclude but game endings for the most part can be almost inconsequential to the overall experience - whether it was a good one or not.
That may sound like a bad thing in terms of story design, but really it makes games unique in the entertainment stakes, as players are just as likely to have a great time sampling a snippet of a level then they are the whole thing. That's why game campaigns are so long as developers are ever eager to keep piling on more features, characters, settings and challenges into their game no matter how bloated it may make them as a whole.
Brothers: A Tale of Two Sons is the antithesis to this approach.