:You could have an AI player with you in co-op like in perfect dark.
:A function where you could talk to marines and tell them what to do(like attack, defend, follow, guard etc...)
:An item like the torch which would b a hologram that would lure out the enemies.
:A double seater banshee.
: Fighting from a marine outpost with human turrets, with covenant and flood attacking from every direction.

Any thoughts? [spanky]