My first idea consists in balancing the weapons by increasing the power of the rifle and the shotgun:
-Shotgun:The current 1960's Remington Model 870 model has only 60 rpm, and yes it's meant to be used in close range only but even in a face to face situation you can always miss, and by the time you finish loading one more bullet in the guns chamber you'll be dead if your facing a opponent with a rifle or a smg.
TL;DR The idea is changing the current shotgun to a sawed or sawn-off shotgun model that has a 2x(52*) that is able to shoot faster twice without the recoil of the remington.
-Rifle:Enlarge the visibility of the rifle to make it more sniper-ish because it's not really fair that a smg and a rifle have the same range, maybe adding a scope or something.
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Silent spading- Simple idea, I think it has been requested, but still, dig or tunnel with no noise by pressing v while digging,because the current spade makes too much noise and ruins the "surprise factor".
Example, sneaking behind the enemy lines and taking their intel
Pic related
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I agree with more ideas that have been suggested but this is a simple game, which is already fun without all the classes or the med kits, etc.