Fairyland

They were driven out once. The world changed; the magic went away. Now, the stars are right and the ancient mounds release the hosts of Otherworld. We're all to familiar with zombie and vampire apocalypses, and I've given other monsters their fearful day in the sun, but now let's consider the revenge of the Good Folk: the Faerie Apocalypse.

So Nuada from Hellboy II (or someone a lot like him) gets their way and a lot of terrible and beautiful (but mostly terrible. Basically think of things from del Toro's other faerie movies--Don't be Afraid of the Dark and Pan's Labyrinth) fae are loosed upon the world.

A game set in this period is more War of the Worlds or Walking Dead. Ragtag survivors are combating magical fairy hordes as best they can. Move a bit more into the future though, and you get something I find more interesting: the post-fairy apocalypse.

In this setting, the faerie would have overrun the world (possibly setting up new Medieval kingdoms and the like--or not) turning into a new Fairyland. Humans might be subjugated (like in Killraven, Planet of the Apes, or DC's original Starfire), or essential hiding in redoubts that provide protection from the essentially disorganized faerie (something similar to Vertigo's new Hinterkind or maybe the post-alien invasion series Falling Skies, if humans have more a resistance left). Playing up the Medieval element here (the faerie's struck against industrial society the hardest, maybe) might give you something like El Cid crossed with Moorcock's Hawkmoon novels.