Galaxy 2 also has a lengthier lifespan than it's forebear. After the player obtains 120 stars and defeats Bowser, they are given the 'Green Star Challenge'. Similar to the coin challenges in the 2D Mario titles, there are usually three new green stars put into each stage that the player must obtain. 122 new stars are spread across all seven worlds; while some are easy to find and in plain sight, others would lead one to believe that the game designers were more than slightly sadistic. Though nothing is gained from getting every star, it does much to lengthen the game and is a worthy challenge.
Is Super Mario Galaxy 2 the best game on the Wii? That's debatable. It is however, one of the best Mario games ever.