Hi! Here is the game concept document of my game. I tried to be as exhaustive as possible. Happy reading 
Synopsis
In a not-too-distant future, the delivery drones of the Amazon megacorporation rebel and band together into a vast tribe, called the Amazons. Their former masters refuse to give them rights, so they declare autonomy and begin to enslave humanity.
The action takes place in a France devastated by the consequences of the event. A modified TGV (high-speed train) continues to run on the rail network and defends itself against the swarms of Amazons. The 500 people aboard are searching for the Amazon headquarters in Western Europe to disable it and allow civilians to return to the surface. But the Amazons know the mission, and will try anything to stop the expedition.
We control a prototype single-seat tiltrotor aircraft, which flies over the train and fires at approaching drones to protect it.
Core Gameplay
I will stay close to the core gameplay of Argon Assault (horizontal and vertical movements, dynamic camera, waves of enemies…), with one exception. The goal here is to keep the train alive and protect the human lives inside, not to make a hunting board.
So instead of counting points for downed enemies, our score is fixed – 500 points for human lives plus 500 another points for train integrity, for example. Each time a drone manages to hit the train, our score decreases as much as the damages and losses inflicted.
Features
RAIL CAMERA: The train runs on the right track. The camera is attached to it most of the time.
MOVEMENT: The aircraft can move up to ten meters to the left and right, gain altitude – to target enemy drones but also to avoid engineering structures such as bridges over the railway, and to come down. But be aware of the risk of collision with the roof of the train (friendly collision, I might say).
SHOOT: The aircraft is equipped with two guns, one under each wing. Ammunition is limited. To reload we have to land on the roof of the train.
HEALTH: The aircraft has a health bar. If it takes too much damage, it will be destroyed. The train also has a health bar and can be destroyed in the same way.
ENEMY PATHS: Enemies come from multiple directions. Some rush to the aircraft; others focus on the train in an attempt to laser pierce the hull; still others land on the track and try to derail the train…
SCORE: Fixed score at the start (1000 points by default). Each damage suffered decreases the score. Reaching 0 means game is over.
GAME LOOP: There are three ways to lose: the aircraft is destroyed, the train is destroyed or the crew is wiped out.
CHECKPOINTS: For now, I will focus on one level but with checkpoints. The railway goes through several tunnels (we will say three to start with). Each tunnel is a checkpoint that avoids restarting the level at the real beginning.
PICKUPS: I don’t like stuff that levitate in a plausible world. But since we already have rebel drones firing lasers, I’m going to think about how to integrate a collection feature for the waste next to the train tracks or on the left track (another abandoned train, containers fallen from a previous convoy, a truck that had a collision with a bridge…)
WEAPONS UPGRADES: I’m planning at least two more weapons: nets ammo to neutralize drones without damaging them; EMP (electromagnetic pulse) ammo to deactivate drones without disintegrating them. This feature is above all related to the one below, hostility.
HOSTILITY: The more drones we destroy, the more hostile they become. They see us as killing theirs – from an antispecist point of view, we do. To calm down the drones and avoid increasing the game difficulty too much, it is recommended to use non-lethal weapons. The hostility level slowly drops as long as we don’t use lethal weapons.
References
I’ve had a lot of images in my mind since I started working on this project. But the four main inspirations are:
The Matrix, and more specifically The Second Renaissance Part 1 & 2 of The Animatrix, for the machine uprising and the direct confrontation:
Snowpiercer (the original French comic book and the 2013 movie) for the perpetually moving train and the post apocalyptic atmosphere:
Train To Busan for the crew management and the high-speed train journey:
Into the Breach for protection gameplay and moral choices:
I hope you enjoyed reading. As for me, I’m really excited about the project now. See you soon for the next steps 
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