I always thought a game with these 4 races would make a fun urban rts:
Martian war machines - No construction or base building, Start with a set amount points and never gets any more that they have to use to buy war machines that are sent from mars. Similar to war of the worlds. This race is about a few set piece super units and careful battle field tactics. So you might have a enough points to call in 3 walkers on a map but once they are gone they gone.
Ninjas - Fully customizable units that rely on stealth and quick strikes. Hidden bases with quick travel build options around the map. Limited to only a handful of units on the battle field at a time.
Zombies - Aggressive neutral race uncontrolled and attack everyone else. Slowly spreed throughout the city unless contained. Danger to everyone but the martians. Martians can spreed the zombie virus and indirectly control them with the right unit.
Human Soldiers - performance based resource allocation points which determine the size and units within the army. Can build defense bases and command posts. Instead of building individual units you plan and build entire squads or divisions and then deploy them as a whole to the battle field provided you have enough RAP available.
The idea was that all 3 playable races played completely differently with different goals. Game play was more victory point based as well. So while the army is defending city streets from the zombie horde and alien war machines the ninja's are robbing banks, killing vips, or taking out units on both sides.
My three most hated aspects of rts games though have always been:
1 - Winner goes to first move advantage - whoever comes out the best from the opening attack is most likely going to win.
2 - Winner goes to best microer - Whichever player is best a micro managing units is the one who will win.
3 - Tech Trees - Why do I have to waste time leveling up buildings on the battle field. Let me choose my tech level and initial setup before the battle starts with army points or some other system.