As a rough estimation, Miyamoto has stated that approximately 90% of SMG2's levels are new meanwhile the rest are all "new variations of the worlds in Super Mario Galaxy" like with new objectives and such. He also says that the addition of Yoshi isn't the only thing that'll be new with this sequel. Miyamoto says that there's something being planned for a new ability for Mario that's "something...a little bit ghost-like but still a little different." Let the speculation begin.
E3 2009 >