7. The Fog
As we've already seen, Greg Nicotero loves paying homage to past horror movies, and he accomplished that again in the midseason finale.
When the tower falls and the walkers descend on Alexandria, they're seen as shadowy figures walking through a cloud of dust. The idea here is that Nicotero was paying homage to The Fog, John Carpenter's 1980 horror. If you've seen The Fog (or you can just look at the video below) then it's fair to say he captured the look and feel of it really well.