So, here's an idea:
1) fantasy-based. I often find it interesting when a game uses earthly terrain with fantasy races. also, using fantasy races would prevent being forced into some cliches and such.
2) all races are controlled by AI (yeah, that's a bit tricky. weakest point of my idea)
3) players play as gods, governing certain nation or race (here not using real-world nations comes in handy). Gods receive mana by worship of their people (amount of priests, amount of temples, etc.), levels from advancement of their race.
4) players would be able to pick god's "class" at the start, which would set god's abilties - god of war, god of fertility, god of trade.
5) god would be able to incarnate into an avatar, gaining direct influence
6) certain creatures may exist (like ancient chtonic monsters and such), that can only be damaged by god himself and can possible damage the god.
7) certain artefacts may exist, which would grant the god certain perks, when acquired by the race
8) god may create "omens" or something, which his nation would be attracted to (send a crusade, for instance), giving the god certain level of control.