For the player:
No hud at all so: No uav. No remote cameras. No equipment loadout / ammo counter information. No friend/foe identification (better know the uniforms). No friend/foe identification broadcast (your teammates better know the uniforms especially with FF on). No incoming communications, either voice or chat. No hit marker. No aim marker. No kill/death notifications. No award notifications (streak rewards or bonus points). No warning that someone has planted a bomb or captured a flag (until emp is over). etc etc.
Also: No rds/acog dots. No thermal/IR. No c4 (radio transmitter wont work). Unused electronic equipment and unplaced streaks disabled (no guided missiles, jammers, clays, sentries, anti-air etc) until emp is over. No outgoing commo so no streak calldowns.
Counter: a perk hardened against such things, possibility built into something like tactical protection that includes flash/stun protection.
Against all autonomous equipment:
Simply dead and no longer works for 30 seconds or whatever the time is.
In other words, you are thrown back into the stone age and are all alone. Since most of that is hud related no its not too powerful. Tell me why that is not useful?
