I think it will have to be about twice as long as OoT, if it's really possible to get 70 hours out of it. I expect a lot of the difference to be sidequests, but if they don't make the main quest a lot longer than WW, I will be extremely pissed. If you don't count padding like the sailing and redundant content, a straight run through WW takes less than ten hours (and not a single game-over, too, which is ridiculous). We don't get Zelda very often, I want it to last a bit when it arrives.