Yesterday I finished Super Mario Galaxy with 121 stars with both Mario and Luigi.
At the end, I didn't realize how much Luigi's perpetual slipping and sliding had affected me until I played with Mario for the 121st star again. Mario handles like a dream. Luigi is a nightmare.
Up next is Super Mario Galaxy 2, although I may just go ahead and skip to Super Paper Mario and then backtrack to Super Mario Galaxy 2, just for the sake of variety.