Zombies are the new Nazis.
Think about it. Nazis have been the de facto bad guys in popular culture for the last 50 years. They are a perfect enemy; nobody gets offended when you have to kill them. Castle Wolfenstein illustrated this in interactive 3D, and the videogame boom as we know it was born.
I think, however, that we've reached a point in our society where the evilness of Nazis has lost a bit of its power. The videogaming generation did not grow up in WW2, and neither did its parents. When you kill Nazis in videogames, you're not avenging the horrors of the Holocaust anymore, or freeing Europe from the tyrannical grips of a monster; you are killing bad guys in order to make it to the next checkpoint, and Nazis have always been an easy target for game designers because (a) you don't have to worry about cultural sensitivity issues, and (b) who doesn't enjoy killing Nazis? It's just that most WW2 games these days don't really focus on the why; they focus on the experience of the soldier in the middle of the battle, rather than the reason why the soldier is over there in the first place, and as a result, the enemy Nazi soldier is no longer as capital-E Evil because they all look the same and there's so damn many of them.
Enter the zombie.
Zombies have been around forever, but I would point to the 2002 film 28 Days Later as the source of the current zombie revival. (My own personal interest in the coming zombie apocalypse was not borne from movies but from Max Brooks, whose Zombie Survival Guide and World War Z made for highly engrossing and informative reading.) Danny Boyle's film reimagined zombies as less of a slow-moving, brainless dread and more of a HOLY SHIT IT'S COMING RIGHT AT ME AAAAAAAAAA horrorshow, and it seems to have struck quite a nerve; now there's zombie films and games all over the place. In fact, one need look no further than a bonus mode in Call of Duty: World At War to see the ultimate crossover - zombie Nazis.
I bring this up because I spent a highly entertaining hour yesterday with 2 close friends killing hundreds upon hundreds of zombies in Left 4 Dead, and it occured to me in the crazy dreams that ensued later that night that a zombie horde is, in 2008, a far more frightening prospect than a Nazi ambush. And it's also a much more fertile idea for game developers. Nazis can only exist in Europe in the 1940s; zombies can exist anywhere, at any time, and they don't need guns to kill you. They have no political agenda or ideology, they have no apologists, and they never run out of numbers. They can be fast or slow; they can be subhuman and superhuman. ALSO: they can be hilarious (Shaun of the Dead, FIDO).
I'm not saying that Nazis aren't evil; of course they're evil. I'm Jewish, fercrissakes, I'm not suggesting any such thing. I'm simply positing that there will eventually be more zombies than Nazis, and we should all prepare accordingly.