Can a game be both revolutionary and nostalgic? This has been the paradox that has stifled game developers for many years. The art of excellent game design is to try to introduce something totally new that the player has never done before, yet make sure the player does not feel overwhelmed by the overall experience or in other words make the player feel comfortable by giving them a sense of familiarity while playing.
That perfect balancing act of innovation versus familiarity is what separates those games that remain timeless classics from those that age with time. In the case of Super Mario Galaxy it not only achieves that state of Zen like balance, it thrives in it.