FPS. Everyone has a jetpack, a laser pointer, and a melee weapon.
There are stationary artillery pieces that can be used by players. They come in various sizes, firing different projectiles at different rates. (HE [big boom], Napalm [small damage/time to deal with transported pieces], AEGIS Chain gun [shoot down shells] maybe?)
Flatbed loaders can pick up arty pieces, and move them around. They must be un-deployed from the loader to fire.
Heavy lifting drop ships can pick up the smallest of the guns, and move them around.
Game play would revolve around inflicting a ridiculous amount of damage on the enemy base/power core. Players can move around wherever they want on the large map, and laser targets for their teammates in the big guns to take out. It would basically be a big 3d artillery game, of much fun. The guns would have to move around to get into a firing position on the enemy core, which means they would have to cover each other, fire on enemy targets, and move close enough to lay the hurt on the enemy base.
What say you all?