So in 2005, a spec sheet was created for “Super Mario Revolutions”. Koizumi explained, "The concept was to play with Mario running around on spherical objects – something Miyamoto had come up with 5 years before, and something I came up with too. Why spherical worlds... What distinctive features attracted us to spherical worlds? Was it just because they were novel?"
He went on to explain more elements of spherical objects and what new ideas they bring to the platforming table.
Galaxy also adds two new actions only possible with Wii -- one is the spin attack, and the other is the use of the pointer to gather stars. The spin attack provides an alternative for players for whom mis-perception of depth makes it a challenge to stomp Goombas. The spin fulfilled other roles as well, like launching coconuts or twisting a screw. "You could use the spin for almost any interaction where you didn’t know what else to do," Koizumi added. "The spirit of simplicity we used in Jungle Beat comes out very well here."
The article talks at length about the thought process behind the game and a number of others, its well worth a read if your interested in game design and what happens behind the scenes. Find the full article over at Gamesutra.