As we posted previously, Miyamoto said that the original plan was to "essentially create new variations of the worlds in Super Mario Galaxy." But, over time, the developers have had so many ideas that Miyamoto estimates that 90% of the game's levels are all new. The rest, he said, are levels from the original Mario Galaxy with different objectives.
The controls haven't changed, but Mario's been given new abilities via the addition of Yoshi and a drill item. Miyamoto also told Kotaku that "there's something that might be kind of a little bit ghost like but still a little different."