Known facts from E3 Gameplay by Azim Petra
Commander mode returns
Players will be able to on the role as a commander, an extra seat to the 64 player multiplayer game.
It uses a ranking system, the more you use it the more experienced your commander will be.
However you have to be at a certain rank to be able to jump in the Commander Seat.
As a Commander, your duty is to give orders to your Squad Leaders and Support the Team using the Assets that you gain from the Points that's been capture by your team.
Each capture point grants different Assets.
Scan UAV - Auto-spots enemies in the area.
EMP UAV - Hides your allied units from the enemy radar and prevents them from being spotted.
Vehicle Scan - Spots every enemy vehicle in the map.
Tomahawk Missile - Sends a Tomahawk Missile to the target point.
Infantry Scan - Spots every enemy infantry in the map.
Deploy Gunship - Sends a gunship to encircle an area. Needs player to gun the turrets, can also be used as a base jump platform.
Vehicle Drop - Drops an armored vehicle into the battlefield.
High Value Target - Marks the target unit for all allies to see.
Motion Sensor
Makes a return for the Recon Class. It detects enemies within the radius on the minimap. Essentially a throw-able T-UGS.
XM-25 Airburst Grenade Launcher
The XM-25 makes a return to Battlefield 4 from Battlefield Play4Free.
This gadget is available to the Support class. It's uniqueness is the ability to explode mid-air, making it great tool for clearing doors/rooms/windows.
Sprint Swimming and Dives
You are now able to swim faster by pressing the Sprint button and Dive underwater by Crouching. While dive makes you swim at a slower pace it lets you retain the stealth factor.
Reloading and Clips/Magazine
Reloading a gun will now throwaway the clip/magazine completely. Any extra bullets in them are not salvage-able. You still can keep a bullet in the barrel by reloading before using all of the bullets in the clip/magazine.
The same applies to Vehicles. Also vehicles now has spare ammo in the rack, each reload is fast but rearming the ammo rack takes longer.
Smoke and Debris
Once the skyscraper has fallen, the smoke and debris are to stay for the whole round.
7 5 Flags on Conquest
Siege of Shanghai has 5 capture-able flags.
Squads of Fives
Each squad may have member for up to 5. Field Upgrades, also better known as Squad Perks are earned through team assist. Once a squad is wiped, their squad perks are revert to zero unless it has been to perk level 3.
Scope Glint
Sneaks it's way into Battlefield 4, while it's not as obvious as it were back in Battlefield 3.
Scope Zeroing
Zeroing your sights is now available. They probably brought it in from Medal of Honor: Warfighter. To zero a sight means to 'tune' it dead center, like something like a ruler, you want to make sure the distance is correct, while on scope this means you can adjust the scope to compensate the bullet drop so you don't have to aim above the target as much depending on the settings. To zero your scope in-game is simple as hitting a key(default key: V). Although i'm not sure what are the settings are or the max range is for the setting, it is still a great addition
Max Range is 1000m(?) still unsure but credits to JackFrags(Youtube).
Suppression Effect
Also made it into Battlefield 4, it has less blurry vision and doesn't affects the deviation as much but the recoil or weapon shake/offset. Whenever you are suppressed, it is as if there's an explosion near you and that will bring your gun down even if the player was aiming dead center. It seems only LMG can produce BF3 style suppression while other guns has it toned down. Also it's more about where the bullet lands and less about how close it flew by the enemy soldier.
Light Machine Gun(long range only?) and Sniper Rifles seems to be the only handheld gun that can produce these effects.
Edit2: All guns can suppress enemy infantries but LMGs, SRs and Other Heavy weapon suppress an enemy infantry longer compared to other fire arms.
Vehicle Performance
Vehicles are now 'heavier', by that i mean they feel realistic or authentic. Turrets are slower, vehicle turn rate are somewhat believable and it has momentum.
For example the waves created by the falling skyscraper, you are actually pushed away or are riding along with the waves.
Or a helicopter taking a dive will certainly takes sometime to slow down and stop to hover.