Working on the kernel of the idea for No Man's Land - Mutant Front I've come to see there are certainly a number of campaign ideas/models available that can really effect how a campaign plays out. Here are my ideas in brief:
The Six-Finger Brigade: The chemicals of the war have caused catastrophic and amazing changes among some in the military and civilian populations. General public reaction is horror leaving the military and governments are struggling with a host of issues. One solution is the newly formed and almost secret "Six-Finger Brigade" composed of mutant troops with some Mutant and Pure human NCOs. Scenarios will be specific war time operations like raids on munitions plants, airbases and mad-scientist laboratories in addition to leading the boys over the top to take on the enemy.
Players in a Six-Finger Brigade should be mostly Mutant humans with the occasional Pure Human. Mutant animals are common or recognized as sentient in the beginning of a NML-Mutant Front campaign using The Six-Finger Brigade setup. Mechanical men should be confined to the status of monsters/NPCs at the start of such a campaign. Most weird-tech will be unusual and even un-invented and be introduced as the campaign rolls along.
Most of the World is relatively intact in a Six-Finger Brigade modeled campaign, the plague bombs haven't fallen yet but may indeed do so at some point.
A Six-Fingers Brigade campaign isn't really post apocalyptic it's more apocalyptic with plenty of chances for freaky science and mutants.
All Quiet on the Mutant Front: Mutants have been with humanity for a generation now and the first children born with mutations are now adults able to fight who are pressed into service. Many futuristic wonders are common and PCs can include the occasional Mechanical Man. Mutant animals are used as war beasts but are not yet recognized widely as thinking beings.
The struggling militaries of the world are hard pressed to mount major offensives so the war has wound down to a low intensity conflict where deserters and looters can often be a more serious issue to deal with then the enemy.
War Without End: The war has been on so long there is seldom any difference between the military and civilian governments anymore. Some minds think the war continues so the population that has survived the plagues and economic depredation of the war don't question the authorities or look to make something better. Thinking beasts have been pressed into service and some fight alongside more traditional mutant and human forces. PCs will be desperate combatants fighting for a few yards a month and dealing with renegade communities unwilling to support the war effort.
Weird high tech seems to be all over the place these days but supplies are unreliable and forces can find themselves fighting with every weapon ever deployed by man.
It's Over Over There: The war at least all the prospect for major battles seems to be over. Nations have all but collapsed and military units are often the only authority. Vast swaths of the past battle grounds are hideously dangerous but can also hide goods few have dared to reach for until recently. Plague bombs have left some cities ghastly graveyards that haven't been surrendered by those changed by contamination and those that refuse to stay dead. PC's are bedraggled veterans or stalwart holdouts refusing to give up on the remnants of the past. Nothing is in ready supply and each winter brings the threat of famine on an ever shrinking and desperate population. The gadgets of the past are falling apart and less understood as those trained in their use die off. For many there is no home to return to their entire lives having been the war and it's struggles, is there a life for them out there?
Shadows of War: The war is long over and a distant memory. Civilization is fortified towns shut tight against ravaging hordes and cruel beasts. Ancient munitions litter forgotten battlefields and feudal lords may rule from an ancient redoubt surrounded by barbed wire and disused trenches. Aside from a different range of artifacts and a setting that may be vaguely recognizable this is mostly a straight-up Mutant Future campaign. PCs are explorers, scavengers and adventurers as they are in other mutant futures.
So there are the campaign ideas. A campaign could explore more then one of these and some aren't' too radically different from each other on the tactical level. If one wanted to play a march-of-time campaign it could shift from one campaign model to another as time marches on.