Completing Metroid Prime, then linking it with Fusion, will allow players to play through Prime again with the modified suit Samus uses in Fusion. It's not yet known whether the suit has any extra features, but it will certainly be nice to see the new suit in full 3D.

Perhaps the more exciting feature becomes available when you complete Fusion. Linking it with Prime afterwards will unlock the original NES title, replacing the dodgy password save of the 8 bit game with a save slot on the GameCube memory card.

Unlocking the original NES title sounds great, the new suit feature may not be incentive enough to play through Prime again though, unless of course it makes some sort of difference to the gameplay.