Zelda's mix of series reputation and sales potential probably couldn't be matched by any one game. Personally, I'd take a Metroid over a Zelda any day, but that series is a lot more niche. At the same time, though, given the lost cause that is Wii U hardware sales, I don't know that that means that much. A new Mario could bring mainstream appeal, but its impact would be muted by how many of those we've gotten in recent years.