First of all, i'm really impressed with how much potential this game has!!!
I know everyone has suggestions but here are mine.

A key you can hold down to run up hills without jumping, perhaps a limited sprint ability with stamina bar. So similar to holding the freerunning button in Assassins Creed, but only capable of going up single blocks.

When a player is killed they bloody the block underneath them a and a few around. This will be awesome to see the changing battlefield and also indicate the death traps with red bloody ground.

Ability to dive and go prone. This will just feel rad if you can sprint and then dive for cover and slide a little.

Blocks take a very small increment of damage from bullets? So a bunker under heavy fire will slowly fall apart.

Killing a player or stealing intel nets you points that you can spend on things like airstrikes and whatnot. Ala Call of Duty.

Bodies litter the battlefield? Limbs blown off or some kind of bullet hit decal on players so you know where you are hitting them.

Simple smoke decal rising from grenades and future explosives.

Mounted machine guns and all that jazz that everyone suggests.