Do Du think I should buy super mario galaxy?

Im not sure to buy it cuz it seems to me there are only levels. I loved super mario sunshine cuz u can walk trought the city, talk with a lot of ppl ecc. Is mario galaxy beautiful too? And do i have to buy the 1 oder the 2? Ik the 2 is Mehr beautiful but will i understand the story even if i didnt play the 1? Thanks to who will answer :)