True Mario games don't come around all that often. In 1996 we got Super Mario 64, In 2002 we got Super Mario Sunshine and later in 2007 the Wii will get Super Mario Galaxy. With history suggesting that each Nintendo home console only receives one true Mario game in its lifetime, there's more than a little bit of pressure on Mario Galaxy's shoulders.
Super Mario Galaxy feels much fresher and more innovative than Super Mario Sunshine - a title that promised so much but disappointed many upon its release. Many gamers expected something to significantly eclipse Mario 64, but take out Mario and you would have been left with just another adequate platformer.