Firearms (CS mod):
Magazine retention and consolidation:
Ammo shown as number of magazines, non-empty magazines stored, ability to consolidate ammo, turning six magazines with five rounds each into one full 30 round mag, etc.
Reloads become a tactical choice, as reloading too often will result in having to spend time consolidating half-empty mags to avoid suddenly reloading a ten-round mag.
Leftover round in chamber:
Dry[footnote]Magazine fully spent, bolt catch locked to rear[/footnote] reloads and Tactical[footnote]Magazine not spent, weapon still loaded and ready to fire[/footnote] reloads shown properly.
Dry versus Tactical reload becomes increasingly important, as reload time can be reduced by reloading prior to completely expending a mag. Tactical reloads also result in a round being left in the chamber, providing an extra round upon succesful reload, and the ability to fire a single shot, while reloading, resulting in a diminished reload speed, as per Dry reload.
Fallout: New Vegas: (Not the first, but the best example)
Multiple ammo types:
Multiple ammo types. Selecting the right round for the job becomes an art.
Pretty much self-explanatory. Just another gameplay variable, albiet a relatively minor one which at any rate only really applies to "slow" shooters such as F:NV.
Hidden & Dangerous 2:
Inventory weight system and carrying limits:
Everything carried lowers overall sprint-time, general mobility and movement speed.
Being able to lug six rifles around is BS, but limiting us to a Primary and a Sidearm is just as BS.
H&D2 limits you to two large weapons. Your shoulder, and your hands.
Sidearms can be packed on the belt or in a backpack, and cannot be equipped while still holding a large weapon in your hands.[footnote]No, holding the rifle in your left and shooting the pistol with your right isn't gonna happen.[/footnote] Extra weight slows you down.
Multi-mission cross-overs:
Three part mission, equipment limited by weight. Explosives needed for third part.
You need to blow something up in the third part. Do you bring your own explosives, letting the weight drag you down in parts one and two, or do you rely on scrounging it sometime during the mission? The choice is yours.
ARMA:
Sniper rifle range adjustment:
Shooting at 300 meters, and then 800, requires an adjustment of the scope, or manual adjustment by overshooting.
All combat optics, even red dots, have a preset range adjustment. High-magnification scopes designed for sniping are usually adjustable, to compensate for bullet drop over long distances. Judging said distance, without a rangefinder, can be a great gameplay element, resulting in more skills needed for sniping.
General observations:
Combatting chest-high walls:
Giving players a consequence for getting hit without dying could effectively render suppressive fire a reliable way to cross open ground, without relying on chest-high walls.
Ahh, the walls. We all hate 'em, right? Regenerative health is a major contributor to the effectiveness of the walls, given that most players can move from cover to cover in too short a time for an adversary to score enough hits. Crippeling the Sprint function and reducing a players run speed to 50% or less for 1.5 seconds after getting hit, and moving his/her aim 15-20 degrees in erratic motion, could make finding enemies at a distance and providing suppressive fire a vital component in multiplayer, resulting in less rambo, and more teamwork.
(Just remember to include Voice)
Weapon retention:
Weapons from previous mission carries over into the next.
Homefront is the most recent game to do this to me. I get the two weapons I like the most, the mission ends, and suddenly I'm back to one I hate. In some games, it's justified, but in the case of Homefront, it's simply not good enough. Fix it!