It might be what started its popularity, but not what kept it alive for this decade.
Cs will be destroyed if it will go towards realism.
*Sound play would be destroyed, because unless there is direct open path to target, sound will reach your ears through ricochets, making it too hard to pinpoint direction, let alone position.
*grenades would be OP, flash grenades would keep blind for entire round, HE would kill instantly, smoke grenades indoors would fill up everything. Molotolovs would make players to fall in agony, jumping out of flames and rolling over to put out flames.
*One hit and players would be in agony, rolling over for destroyed desticles, unable to hold weapon when arms is shot,etc.
Ar, interesting topic, but Idk if there is point to continue :D