I don't own any FPS's for the Wii, but Super Monkey Ball has a Mini-game called "Monkey Warz" that is an FPS Death-match style mini-game. Maybe it's just me but the FPS Controls for that are pretty good....
Left analog to move forward/back and strafe left/right, c to crouch, a to jump. The wii pointer is used to look around and aim, but to look left/right you have to move the cursor closer to the edge of the screen. You also have to make a throwing motion to throw bombs and other junk.
I haven't played it much but I mean the controls seemed WAY better then Gears of War's, Halo or any FPS i've played with a regular controller...and this is a Mini-Game in Super Monkey Ball!
The potential is there, point-and-shoot aiming for a gun is infinitely more immersive then using analog sticks to lineup a cross-hair.