The Wii games are largely gimmicks right now. That will change as developers learn more how to use it. You might get tired aiming your gun in Metroid or Red Steel for hours on end, but that could just mean shorter play sessions.
If the Wii sells as well or better than the competition, there will be plenty of devs jumping onto Wii this winter. It'll take a year or two before those new devs finish their games (like DS), but they'll eventually get here.
If motion sensing in Red Steel and Metroid is too difficult, it can easily be dropped. I think we'll see some standard gun games, as well as gun games where you basically just shoot with the right hand and move with the left. Devs will figure it out eventually.
