Re: GW Inspired Video Games
Had it been me, I'd have gone for a persistant world FPS like Planetside.
Imperial, Chaos, Eldar and Orks as the factions. Set it during the Black Crusade, so you have a logical reason for everyone fighting.
Different regions .. jungle, artic, desert, hive cities, underground caves and tunnels and orbital stations.
Probably do something like Planetsides skill points, where when you level up you get access to another skill point, and can buy the ability to use different weapons, equipment and vehicles.
No quests or missions. Just take the territory and kill the enemy.