Speaking behind closed doors at E3, Shigeru Miyamoto has stated that Super Mario Galaxy 2 is based on "about 90 percent" new content.
Speaking about the development of the original title, Miyamoto said:
There was so much more gameplay we weren't able to use, and we were a little disappointed. So we thought what the heck, let's make Super Mario Galaxy 1.5. But once we got started, the team got so excited and started making all of this new stuff. More than 90 per cent of what you see in Super Mario Galaxy 2 will be brand new...maybe closer to 95 or 99 per cent.
While this all sounds very promising indeed, Miyamoto also commented that the amount of play time the game contained would be roughly the same the as the original - which is still more than enough for most gamers.