My dream is a fallout game set in New Orleans, but made by Obsidian.
Give them permission to have greenery in the game as you run around a massively overgrown swamp (there's some lore from unpublished games about an over-abundance of GECK testing in the area,)
Helping people actually build new shit from the abundant trees. The people would be that fun mix Creole and Americana.
We could have new enemies, like snakes and gators and shit. Maybe assassin vines and man eating trees.
My dream enemy would be a splinter group of Caesar's legion and remnants of the Enclave.
As for music, dig deep into New Orleans history. There's more than enough to put together a kick-ass soundtrack.