Fantastic! I don't think I've seen you pay this much attention to background before. You'd better be making these each in individual wallpaper size. The one on the top left looks like an especially nice place to call home for some reason.
The first one looks like a dwarven forteress at nightfall, the second one looks like building on a harsh and unforgiving Forgeworld, the third one looks like a crag were Orcs and Goblins would live, and the last one looks like Ulthuan