Brawl is everything that makes Nintendo culture great: the characters, the humour, the heritage. Want to show someone why you've stuck by Ninty all these years? Show them a portly plumber chasing a green dinosaur with a massive hammer.
But Brawl also represents Nintendo as a company. Returning to your stock franchises guarantees games a heritage like no other; likewise it shackles you to old ways. Brawl is sublimely tuned and inexhaustible in its attempts to make you happy, but it's not new. But this is by no means the end of the world. Sakurai is saving his masterpiece for that one.