This guy has put up YouTube videos of the first hour of Metroid Prime 3 gameplay. Obviously there are spoilers, so don't watch if you don't want to know what happens at the start.
http://www.tehgamr.com/2007/08/19/first-hour-of-metroid-prime-3/
http://www.tehgamr.com/2007/08/19/first-hour-of-metroid-prime-3/