One reason I think it will be a big success is because of the fitness factor. Natal will be far superior to WiiBoard. The freedom from the board to track exercisers will be a huge benefit. Wii Board really doesnt work very well with more intense exercises. I think this will lead to the people that want an interactive exercise tool to move from the Wii to the 360 with Natal. Now that means I expect one of the titals this fall to be a Natal fitness title. The should even bundle it with Natal.
Its libraries that sell systems not a single game.