Conquer or hold checkpoints through New York! I think this would be great!
Actualy you can do the singleplayer missions in multiplayer mode, one team is the offensive, the other defensive. When a defensive team lost a areas they should have the possibility to conquer it back.
Together with (computer controled) aliens which attacks both teams, helicopters to drop squads deeper in the war zone, vehicles etc..
Such a match would last for several hours, so dynamic environments, like from afternoon, sunset and night are possible.
Should be nice!
What do you think?