Futuristic gladiator-like setting in a gigantic megastructure in space to keep maps from being too grounded and mundane. The host is a fat alien and people (mostly mercenaries) are his toys. They each have personalities, and the player can taunt by pressing the "pick up" button when there is nothing to pick up. Might seem useless, but I have used this in another game to let others know where I was in nearly empty matches, instead of wasting ammo trying to draw them out. No character creation. Toon (but not kiddy) art style, because multiplayer games are silly. Mostly projectile weapons that look logical. Medium-sized arenas, each with layers. Some moving platforms. A couple of lived in areas rebuilt for fighting.
No radar of any kind. No nametags over the characters giving away their locations. No glowing reticle when aiming at them. You tell who the enemy is by the paint thrown/wiped on them before battle. What those colors are would depend on the environments. No surround sound, because most people will play without and be disadvantaged. Friendly fire would always be active and deathmatch modes would have tickets that deplete.
Third-person camera, light but nuanced movement, a slide lasting a few feet when holding the crouch button during a full run, a melee button that makes you swing your gun when on your feet and kick when jumping or sliding, the ability to kick off walls (as well as other players). The full run is not just forward-based; you can dash in any direction and keep shooting where the camera is pointed. The camera shakes a little more in a full run, not for realism reasons, but to handicap their aim and keep everyone from dashing endlessly. In the default movement, the standard slow video game run, the aiming is totally fine. When you dash backwards into a slide, the character will throw themselves onto their back so that they can keep shooting. Rising from prone would not be too fast, or players would be sliding around nonstop. When prone, the player can move sideways by holding aim (right mouse button), but this zooms in the camera. I think Max Payne 3 balanced the default camera with the "aim" (right mouse button) camera (and shoulder swapping) well. Neither was too close nor too far. I would model mine after that, obviously closing in as you move into tighter spaces. You would be able to lie down by holding crouch, like in Metal Gear Solid. Tapping crouch from a full run would make you perform a roll. Pressing crouch and jump at the same time from a full run makes you shootdodge in the style of John Woo but without the slow motion of Max Payne.
To use a grenade or trap, you first need to find one in the environment, then select it with the "grenade" button (which puts away your gun) and finally press the shoot button. You can't just lob one instantly.
Everybody enters the match with a single random weapon. They can pick up the weapons of defeated players and better weapons are also placed randomly on the map over time. They can carry two slinged weapons and two pistols, which can be seen on their character so that the others know what they are up against. You move a little bit slower with one long weapon and then a little slower still with two. There is a different animation set for each level of encumbrance. You can drop weapons.
Pistol/SMG bullets and shotgun pellets don't just disappear at a distance, like in almost every shooter. They just become weaker and stray more off their target. Shotguns have a medium effective range, meaning way farther than in most shooters, with a narrower spread.
You gain a little health by killing. The only way to recover health is to kill. Let's pretend it gives you adrenaline to keep going.
Three types of suppressors can be picked up: sidearm, rifle and shotgun. The suppressors heat up with repeated fire, glowing red before you need to give them time to cool off. Continuing to shoot will just make them break, and then they disappear.
Female characters are available, but they have lower hitpoints and weaker melees. I think this would prevent there being a bizarre number of women in the battle. Tradeoff is smaller hitboxes on the women.
Destruction (mostly cosmetic, but not only), physics and blood and (not overdone) gore are essential. I'm tired of shooters being so stiff, of characters and furniture not being thrown around by explosions. Send me flying and smashing into walls. Be over the top with it. There was a time in Max Payne 3 that I shootdodged away from a rocket, flew over a bus and stood up to immediately gun down two players. Not a good multiplayer game by any means, but I miss those satisfying moments when the game was still fairly active.
Modes:
-Team deathmatch in which the other team's tickets need to be depleted.
-Free-for-all.
-A one versus all mode that pits beginners and bad players against seasoned players with decent kill ratios. The target has the same hitpoints as everybody else. This is more fun than it sounds for the hunted. Think I've only had it happen once with equal hitpoints on both sides. Was weird how the three players just silently decided in a free-for-all that they would gang up on me.
-Some kind of objective-based mode with mixed goals.
-Elimination. No respawns.
A map-maker, because eventually players will grow tired of what's available.