Walking would be the same, using W, A, S, and D.
Barrel Roll - In first person, the player would either jump forward at an accelerated speed OR the camera could sort of do a flip while the character accelerates.
In third person, the character would appear to do a barrel roll at a speed, faster than walking but not quite running.
Taking cover - Instead of hitting SPACE to go into cover, the person would have to hit E to avoid confusion with jumping. The player can take cover while in 4-5 blocks of the wall which could be any height. Holding a WEAPON (check next section), the player would be able to aim around/over the cover by holding the right trigger (I'm just going to say trigger)
To jump over cover, you would tap E while holding the direction key that you would like to jump over in depending on where the camera is looking.
Aiming - When in first person, the gun will already be aimed in the default least scoped position. In third person, the person would hold down the right trigger to aim and spin the scroll ball up to scope in (If available)
Basic Gears of War 1 weapons could be added into the game (Lancer, Gnasher, Snub, Torque Bow, Longshot, Frag, Boltok, and maybe the Hammer of Dawn)
Lancer - Would fire very weak shots at about 10 shots per second with a clip of 50 or 60. The chainsaw bayonet can be used when in melee range. Gnasher Shotgun - Would fire 8 pellets per shot (8 shots per clip) With an appropriate spread so it could not be used as a sniper. Snub Pistol - Would fire a semi-weak shot. (Trigger-finger) Either 10 or 12 shots per clip. (Can be scoped) Torque Bow - Would fire an arrow that does little to no damage on impact but would explode after about .5 seconds with a deadly blast. Longshot Sniper Rifle - Fires a very high-powered shot before having to reload. (Can be scoped) Frag Grenade - You know... a grenade that goes boom. (Players will be required to hold down the right trigger in 1st or 3rd to aim the grenade due to the odd nature of the cross-hair) Boltok Pistol - A high powered pistol that fires 6 shots before reloading. [Very similar to a revolver] (Can be scoped) Hammer of Dawn - Just look at this thing.
All enemies with the exception of The Boomers and General RAAM should be able to be chainsawed with a small physics engine included with blood and guts and what-not.
Headshots should cause an explosion of the head, also with physics included.
A few very basic Ideas I came up with for ammo where putting an iron ingot and gunpowder vertical and it creates 10 bullets. I am hoping for the ability to hold as much ammo ad possible in one stack (Ie 1000 instead of 64)
Torque Bow arrows could be an arrow with TNT or gun powder and redstone.
A shotgun shell could be composed of putting one bullet in ever on of the six provided spaces on a Crafting Table. Maybe there could be a new table.
That's pretty much it, guys. If I think of anything else, I will add it.
If anyone thinks they want to get this started, it's all systems go. Just keep me updated on your progress.