I would say to add in more Galaxies that involve more exploring and things like that. Linear levels are fine, but I would have really liked some more. It would also be great to control the camera at all times and make the swimming levels easier to control.
Currently Playing: Mario Kart 7, Mario Kart 8, Luigi's Mansion: Dark Moon, The Legend of Zelda: Majora's Mask, Super Smash Bros for Wii U
Predictions:
Super Mario Galaxy will pass Super Mario 64 in total sales CORRECT!