I'm also curious where this faith in MP3 comes from.
MP1 sold something like 2 million WW, and then considerably less for MP2. It's not that big of a franchise on the Nintendo scale. I'm not surprised Mario Party 8 is doing well, the series is popular even if it's not among gamers, so I don't see the logic of "Mario Party 8 is selling well, so Metroid Prime 3 must do better".







