Ritz, please remember the nunchaku extension with the analog stick and extra button. Use THAT to move around and jump. Tilt the controller to look around, a la mouse-look. Use the d-pad to change weapons, the A button as a "use" button, and B to fire.
Boom, VERY simplistic FPS. I'll admit the controller needs more buttons for anything more complex, like flashlights (a la Half-Life, not a la Doom 3), but this setup works pretty nicely - in theory, at any rate. At the least, it could pull off a mean Quake. Just update the graphics a whole lot and make it multiplayer, keeping the overpowered rocket launcher, and boom, insta-Halo-killer, just because Quake is awesome, 10 years later.