I want a dark, yet not serious shooter. Kinda like Brink was- neither side was truly good or bad, and the story had some major implications iirc.
Anyway, you've got plenty of in-game factions. Most are fairly dark, such as the "Murder Corps"- black trenchcoats, red armbands, almost Nazi-ish. Their main feature is that you can't see them directly- even the grunts have full masks and gloves, so that you can't even figure out skin color. Later units, sub-bosses, and bosses in this line are often augmented in some way.
Weapons are also not grounded in reality at all times- you've got some crazy stuff like sonic cannons, magic users, the transforming stuff ala RWBY, even up to and beyond mecha, orbital weaponry, gates to heaven/hell...
The game is basically an MMO: choose a side, get to killing. Different modes offer different levels of play- "Heroes" might allow for no-respawn, instant max level, players onnly deathmatch, "Turf War" might be a DOTA-esque mode involving mooks, respawns, items, levelling, and all kinds of fun things.
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As for the ideas below, how about we take the same idea, apply it to the new ideas of "branching storylines in an FPS"?
Practically every mission is going to be taxing on you, leader within the insert-name-here clandestine ops. You and the three other people in your squad are going to go through hell and back for your nation.
The first few missions play nice. Teammates are scripted to not die, and stress is functionally capped to where you'll only get a taste of what doing badly will bring. The training wheels come flying off very quickly however-just as you're finishing up one mission, a loud bang, a whirling sensation...
and you wake up in the ruins of your chopper, barely alive, surrounded by the enemy. As far as you can see, you're the only one alive. They force you to walk, as best as you can, excruciating as you're more than just banged up. The sequence doesn't last long, but it pulls no punches. Blood, carnage, and your three former teammates strung up from the wreckage as groups of your enemies laugh. Then, black.
The friendly mission info that normally pops up giving you the location, time, date, and mission name come up once more. Unknown, unknown, unknown... and Survive.
You'll have to endure various "interrogations" in a Mass Effect style, except wrong answers will hurt your sanity and your chances of escape. The enemy forces use various methods of torture to control you- mind-altering drugs, lack of medical treatment... the list goes on.
After a number of these interrogations, you'll have learned a few things about the people keeping you hostage. You'll also be afforded a chance at escape.
From here, a traditional mission starts... almost. You're at roughly 10/100 HP, it's hard to walk and you stumble about, and you're definitely seeing things. On occasion, your surroundings flash with horrible visages. At one point, you think the floor has grown a mouth and is trying to eat you. You're trying to hold on to your sanity, when a hideous beast rounds the corner and comes after you.
In reality, it's a random guard armed with an AK wandering around, likely on his way to your cell for some reason or another. You, the barely clothed, barely alive, and almost insane hostage, proceed to claw his eyes out and beat him to a pulp, before taking his weapon. The rest of the mission still has moments of drug-induced freak outs, but you've got a gun now. You still can't distinguish reality from crazytown well either, and the walking sway is lessened. What isn't is your ability to control your rifle. You've got a single magazine, and that's it. No silencer. Every guard hearing gunshots WILL home in on you mercilessly, you won't survive a gunshot, and your accuracy is piss poor. You do have the benefit of adrenaline, which makes some actions that seem impossible less so, and you'll be able to get a first aid kit relatively early on. This will improve your surviveability, but you won't regen health, your aim isn't very improved, and you still wobble a bit. Continuing on, the drugs will start to fade, and you'll get this half-reality where some things are wrong but you can tell what things are- metal bar doors may appear jagged, enemies will appear very evil, etc.
To end the mission, you escape the facility by hijacking an enemy truck and driving off. You manage to lose any pursuers, cut to a scene of you driving nonstop and winding up a fair distance from a city in the desert, at night, when you finally run out of gas.
From here, you get fixed up, tell people a modified version of your story, and get reinstated in your old job. The cracks are evident, and people who knew you are a little off-put by the changes. You've got to make decisions, again, under pressure. You've got to deal with the motivations of revenge, the flashbacks, and your ability to fly off the handle when it comes to murder. If you get too stressed, you'll wind up AWOL- and a traitor.
Eventually you'll be assigned with the capture of the terrorist leader. Cue a scene with him sitting in a room, alone, and you come up to him gun waiting.
Another Mass Effect chat. The leader will speak, and what he has to say will wear on your psyche. You're given the option to capture or kill him, or if you did poorly enough, you'll already be beyond rational decision making.
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Most decisions are not chosen by the player and are determined only on principle of stress. A mission where you have to call strikes on terrorist forces? With low stress, you'll be able to do it without much outside help, but too much stress and you'll be ordering in missiles. Stress is gained from pain (taking damage), watching teammates get hurt or die, enemies being successful, etc. Stress is relieved by completing objectives and slightly by medkits.
Gunplay is strong, but melee is even better. Rather than limp-noodle knife swinging, you'll get anything from silent, possibly nonlethal takedowns at high sanity, to anything from neck-snaps to animalistic clawing and stabbing at low sanity. You aim better and see better at high sanity, things wobble slightly, your aim is worse, and you're more likely to misidentify or see strange things when sanity is low.