Planetary Annihilation.How cool would it be if continents were individual moons with spherical shape. No borders. Move in any direction where ever you are. The distance to the horizon would obviously have to be greater than render distance, otherwise vehicles would spend all time popping up and down at the horizon when engaging each other. Flying and compensating for bullet drop in a world with spherical gravity could be tricky. Ignore the size of the buildings. In an FPS game they would obviously be smaller relative to planet. The map screen could toggle between 3d and an interactive 2d projection like this. The shape would have interesting effects on the day cycle obviously. As you move around the map you move through different time zones. Well assuming it's possible to adjust the skybox accordingly. Simulate rayleigh scattering like in the unity game engine. I'm aware that render distance, shooting range and map size and curvature numbers might not work out in the end.
I had this game for 3DO called Starfighter back in the day. The maps were basically normal, but you could fly into the upper atmosphere and see that it was actually a repeating spherical world. The whole thing was seamless and pretty impressive, and this was done on a mid-90's game console.
After a lot of struggle with calculations I realized that in order to have 1000m to horizon for infantry the map would have a circumference of 1500km. Compare that to the 8km length we have now.
Spherical maps would be great. But i guess vanu will complain a lot, coz only weapons with bullet drop could shoot "straight"