The Wii for FPS is awful. It's ridiculous trying to hold that light-as-a-feather controller still. The buttons on it are a bit retarded too. I only like Wii for interactive things. My friend got CoD WaW for Wii, and it wasn't that good.
I would love to see the progress made on that new 360 project, which registers all of your body's motions. Would be really fun to play on it if everything works correctly.