Not too exotic? 
I’m not sure how people would react to a WW2 Earth invaded by aliens movie. I can see the 'pan’s now. Just because it was a decent story doesn’t mean it wouldn’t suck on the silver screen ;).
By “not too exotic” I meant an idea that wasn’t too bizarre to be appreciated by an audience unfamiliar with science fiction. You can easily summarize the idea of World War: aliens invade Earth in the middle of World War II. But most SF works are not equally accessible to a non-SF viewer. Imagine trying to “pitch” something like Hyperion or Courtship Rite to a skeptical producer.