Had an idea for a campaign revolving around a few members of the military helping defend the "North American Safe Zone".
They go out for recon, they find a massive mutation the likes of which no one has ever seen (building sized) rampaging its way towards the Rocky Mountains and the safe zone.
Their vehicle and radio are destroyed, and they must salvage a new one in order to contact their leadership and obtain instructions.
They're told to destroy the thing at all costs, so they get a truck running and load it down with flammables and explosives.
The last chapter consists of a vehicle mission, waves of infected must be thinned out to allow the truck to catch up to the mega thing, in the end a choice must be made by vote, ties decided by the host, they either complete the mission and sacrifice themselves destroying the thing, or veer off and get a "survivor" or "coward" award instead, leaving the north american safe zone to deal with this threat as it comes.