I haven't played Mario Galaxy yet but OoT isn't a perfect game. It will be beat someday... There is a way to make a better game than it.
Mario Galaxy seems pretty awesome... I don't know if it's as good as some reviews say, but if it is I don't see why it couldn't take the #1 spot.
I just find it sad when people cling to memories of a game so hard that they refuse to belive that another game can be better.
P.S. I love Ocarina of Time and Zelda is my favorite game serie... I just think that Ocarina isn't perfect and it can be beat.