Call of Duty World at War has a hidden level called Nazi Zombies. It is addictive as your only mission is to kill as many zombified Nazis as possible. There is no end, they just keep coming. My idea is to take this to the next level and create an entire game centered around killing zombies that just happen to be in World War 2 bad guy uniforms.
Set the game in the late fall of 1944. Western Allies notice the Germans retreated from France and never came back. They chase into Germany to find no troops fighting up to eastern Prussia. Static is all they pick up on German radio frequencies. Many German citizens are in hiding. They also lose contact with the Russian allies. Airplane recon confirms the unbelievable: something zombified the Eastern Front and the non-zombified German units of the Western Front rushed to stop the zombie hordes from advancing. They failed. It's the allies job to kick ass from Berlin until they see no more zombies.
The settings and missions would be bombed out cities in Poland, the Baltic states, the Ukraine, Belorussia, and possibly ending in Moscow. A cool portion would be the besieged city of St. Petersburg still holding out but this time vs. zombies, not just Nazis. The developers could end the game in Moscow or even further, at the Ural Mountains. There could be two person sniper recon type missions where partner mode could allow for a sweep through a small town to pluck off any solitary zombies. Another route to go is making it partly a detective story, as missions could find out how this happened. My gut instinct is to make it a secret Nazi biochem weapon that zombified one battle and all hell broke loose afterwards. Having it be a campaign would allow for winter missions and snow camo, which could be cool as you could let zombies walk by you and then cap them instead of the auto-chase all zombies have in games.
This game would be a big seller as 1. people love shooting zombies 2. people love shooting Nazis 3. people hated the USSR (except some college professors). Shooting zombified Nazis and Commies would be in America's strike zone. Making this an off rails 1st person shooter would be best. The Wii would have to use the nunchuk as well as the shooter attachment. Creating a world would be key, as you could have online play where you team up to take out zombies in Nazi and Soviet uniforms. Come on video game world, make this happen.