You would start on an island with 5 Soldiers, and able to give them classes. you could stay on your own, or join a group, and form a base with other players, a base would not technically need to be owned by 1 person, and in theory up to 10-20 other players could operate out of 1 base.
You would get troops that you train and build up, that achieve different tasks. When a troop dies, they are gone, no saving them, just gone, dead, eliminated, same with equipment, boats, all of it, when it dies, it dies. If your knocked back to the start, you receive 5 troops again to start over.
Your allowed 10 troops in 1 battle at any given point. Soldiers upgrade into different areas, giving different abilities.
Commander, they are you leader(only get 1), they shouldn't typically be on the battle field, they would have assault like troop abilities, what they do is sit in an under ground bunker, where they ok/make trades, alliances, allow you to pick research paths, when they die, you get a new commander, but being a lower level, are less focused on what you upgrade. you may upgrade Ammo, and may end up with a light weight body armor upgrade, that cost 5 times more than it should have. (lack of over sight).
Sniper, They would kill things at far range, obviously not that effective on tanks, but if it has flesh it can be killed by a sniper. the best counter is a vehicle either directly killing them, or troops jump out of a vehicle at close range and kill them. If you have no Vehicle its time to run.
Rocket trooper, they are good at killing mechanical units, and weakly armored troops. They have difficulty against snipers when in the open.
Scout, They are stealthy, lightly armed, they call in air strikes, and can drive small ground vehicles (jeeps and such, not tanks)
Pilot, They fly planes, helicopters, Heavy armor, and boats. When they upgrade, they are allowed to pilot more and more types of vehicles in the appointed tech tree.
Medic/doctor, they heal units.
Scavenger, they gather resources, and are lightly armed. and by scavenge, its off blown up enemy and allied units.
Gunner/master Gunner, they are your turret commanders, for tanks, ships, and land based defenses. They have a range equal to or grater than a sniper, and 5-10 times the range of a normal soldier.
Engineer/mechanic they build and repair your equipment and base structures.
Electronic warfare officer, what they do is hack your enemies, so that there advanced weapons and vehicles have issues when attacking, and not protected by either a electronic warfare officer, or some sort of anti hacker program. They also fly drones, and help locate targets on the map.
Heavy Infantry, large caliber machine guns and tons of bullet proof armor.
Commando, Capable of being parachuted into an area, or swim in from a boat. Requiring no landing craft, or helicopter to be put in danger.
Researcher/scientist, they research you tech.
You would be limited to around 100 troops, possibly 200, or somewhere in between, they would be like your ships. They are fully upgradeable, in terms of equipment and core stats.
The Command center and most of your base is located under ground, the exception being turrets, docks, ships, aircraft, rockets and drones, some energy producing structures. So unless you storm the base, which most wouldn't, due to the face if its a vengeful person they will self destruct the base killing every troop you send in.
Buildings wouldn't be as 1 track, as the other games.... for example your in a under ground base, a huge windmill gives away your position, so once a little better off, make a geothermal generator, some under ground storage, some equipment and research.
You would have an armory for equipment, and a lab to build the equipment, under ground naturally. You would make your own Ammo, and upgrade it. Each type of troop would be able to be researched.
You would have gunners defend your base, if a troop type you didn't want to attack with, lets say a ship is firing at your base, you will hide your snipers inside., however if close enough may send out rocket troops. may send out drones to sink the ship.
When your base is under attack, you can recall troops in for safety.
Each set of troops is grouped together, so for example you can have the base commander with the engineers and scientists under ground where you make new equipment.
You have the above ground defenses in 1 group.
You have your electronic warfare in 1 group.
You have your base guard subterranean defense, so they try and stop any army trying to force there way in.
You can for example research Gunners, and electronic warfare officers. Rather than have each turret manned, you can put an automated fire control unit, that is remotely fired from inside the base. The drawback is an enemy Electronic warfare officer can turn your turrets off, or worse, take control and fire upon your own equipment. You could for example use the hard wired system, with no uplink on a closed intranet, with no wifi ability, and totally isolated, it cant be hacked. but extremely more costly.
You research generalized areas, which have no limit, but certainly have a cost. Meaning you can upgrade a weapon to no end basically, for damage, range, accuracy, so if you have a level 50 sniper rifle, requiring level 50 ammo, a lvl 50 scope, you may have 100 range with it, to do 500 damage on a flesh target, 50 on a armored ground target, 150 on an air target. The accuracy would change depending on the target. so a tank, is easier to hit then a person, and person easier than a mach 2 fighter, a slow moving helicopter or drone is target practice.
Than you need to also upgrade sniper armor, sniper camo, and each troop type has all these things to research.
Ships and tanks, and planes all have aspects to upgrade.
You can reverse engineer found items, need to find 2-3 of the same item to reverse engineer an item.
What a mission would look like
At first you take your own island, and wipe out the npc natives, and possibly invite others over to your island.
You would lead up to 10 troops on a patrol.
likely you will encounter 5-10 npc's, likely a hut, some tech, some ammo, so you will need to take scavengers along.
all troops start out at infantry, which have limited scavenger ability, for example picking up ammo (duh) and enemy weapons, how ever ripping something apart that was destroyed to take out the electronics, finding the hidden stash that is buried, that sorta stuff is all them. or finding an unexploded rocket to reverse engineer it.
you would take a sniper or scout on nearly all ground missions, well at least one. obviously a rocket troop or 2, going to need scavengers, possibly a medic. Maybe heavy infantry, and some assault troops, and a commando if you have one.
When you attack an area, you will know the general terrain, for example if you see plains, time to bring 4 snipers, if you see its all jungle, you will want heavy infantry and scouts, if you see rough rocky terrain, its more for assault troops and rocket troops to blow up the caves. If its in a city, bring the rocket troops, maybe a drone with its operator. Maybe a demolition man to implode a building your enemies are in. basically the terrain dictates what you send, its not as repetitive or predictable, when the enemy is different each time, it makes it more challenging, when you stumble across an enemy camp of 5 commandos in the jungle that are hard to see because of camo, and only found out they are there, because they just shot your medic in the head. its time to run away, or call in an airstrike.