What's new in Mario Galazy when playing as Luigi?

When you complete Galaxy with all the stars you're told that life goes in cycles but it won't be quite the same.



Then you get the option of playing as Luigi - but the game seems identical (although Luigi's perhaps harder to control).



are there any minor differences to the actual game world or challenges?



Are there any other bonuses if you complete the game again with Luigi?



thanks for your help!What's new in Mario Galazy when playing as Luigi?
there is an extra star and an alternate ending! OOOOOOOOOOOOOOOOOOOOOOOOOO!!!!

ALSO YOU GET TO WEAR A GREEN CAP!What's new in Mario Galazy when playing as Luigi?
I think there might be an extra star you can get, but I'm not sure!!!