MOH Heroes 2 has 32 player online multiplayer and reportedly great controls. No offline multi but its a good start.
Now that MP3 has shown how FPS controls should be done hopefully it won't be long until theres some really great multiplayer shooters on the Wii.
Personally i never thought much of Halo, though i never played multiplayer on it. I guess it was good for a console game but not that outstanding as FPS's go.