Grey Goose is a citrus, vodka based, like lemonade I think...
the Gran Marnier Slush is made from Gran Marnier liquour, the Gran Marnier is an acquired taste - and I have acquired it!! not like brandy, not like Drambuie, it does have an "orange" flavor, but its very.... not sweet, not citrus flavor...
DH loves the Gran Marnier slush, I prefer the brightness of the Grey Goose...