GG would be more suited to a 3d plantsVzombies style game where the player has to defend a location against waves of zombies/monsters/aliens/soldiers using a set of weapons that can be strategically placed by the player to defend zones. After each wave any zone containing NPCs that are still 'alive' becomes lost to the player who then has the opportunity to add more defences or re-position existing ones. During each wave the player can re-load some of the weapons or maybe even take control of the aiming of weapons but restricted to one at a time.
The locations could be something like a shopping mall (classic zombie location
), factory, power station, airport etc. The 'weapons' available could be different for each location.
Before each wave starts the player would pick a zone to hide in during the attack, if any NPC manages to get into the zone the player is in then you lose a life, if the players defences wipe out all NPCs in the wave then you get a bonus life.
Been there, done that, got all the T-Shirts!